BIBLIOGRAPHIC REVIEW
ADDENDA TO
COMPENDIUM BOOK
ON SUSTAINABLE AGRICULTURE
FOR THE PHILIPPINES
NASSA CARITAS
M.Sc. Eng. JOSE MANUEL RAMOS SANCHEZ (Ph.D.)
1
INDEX
I.
AGRICULTURE THEN AND NOW - RURAL EXTENSION AND ORGANIC AGRICULTURE...............................................................4
RURAL EXTENSION: AN INTRODUCTION.....................................................................................................................................................4
ENVIRONMENTAL THREATS IN THE PHILIPPINES.................................................................................................................................... 5
HAZARDS OF PESTICIDES.............................................................................................................................................................................. 6
IMPACT OF PESTICIDES ON FARMERs HEALTH AND THE ENVIRONMENT............................................................................................ 7
STANDARDS FOR ORGANIC CROP PRODUCTION......................................................................................................................................13
GENERAL REQUIREMENTS FOR ORGANIC PRODUCTION AND PROCESSING........................................................................................15
II.
ORGANIC AGRICULTURE CAN FEED THE WORLD........................................................................................................................... 36
INCREASED INTEREST IN NUTRIENT BALANCE STUDIES: THE NEED FOR INCREASED AGRICULTURAL PRODUCTION............... 37
EXAMPLES OF NUTRIENT BALANCE ANALYSES.......................................................................................................................................38
CROP ROTATIONS.........................................................................................................................................................................................40
BIOPHYSICAL CONSTRAINTS AND CHALLENGES IN AGRICULTURE......................................................................................................41
GROWING LOWLAND RICE..........................................................................................................................................................................43
STORAGE OF PESTICIDES............................................................................................................................................................................ 47
CAPACITY TO ADOPT ORGANIC CERTIFICATION..................................................................................................................................... 48
RECOMMENDATIONS ON GOOD AGRICUTURAL PRACTICES FOR RICE................................................................................................. 48
APPLICATION OF PESTICIDES.....................................................................................................................................................................49
QUALITY MANAGEMENT IN PRE-HARVEST PRODUCTION..................................................................................................................... 50
CROP ROTATION ON VEGETABLE FARMS................................................................................................................................................. 57
CONSERVATION AGRICULTURE..................................................................................................................................................................58
INVASIVE SPECIES........................................................................................................................................................................................ 60
RICE PRODUCTION IN WATER-SCARCE ENVIRONMENTS.......................................................................................................................60
CROP/SOIL MANAGEMENT PRACTICES TO MAINTAIN OR IMPROVE SOIL PRODUCTIVITY............................................................... 61
GREEN MANURES AND ALLEY CROPPING................................................................................................................................................. 63
INTERCROPPING...........................................................................................................................................................................................63
EROSION CONTROL...................................................................................................................................................................................... 64
TRANSFER OF TECHNOLOGIES...................................................................................................................................................................64
WATER RESOURCES IN RICE-GROWING AREAS....................................................................................................................................... 66
WATER PRODUCTIVITY............................................................................................................................................................................... 67
GERMPLASM DEVELOPMENT AND AGRONOMIC PRACTICES.................................................................................................................68
USING RAINFALL MORE EFFECTIVELY...................................................................................................................................................... 69
EMERGING APPROACHES............................................................................................................................................................................ 69
AEROBIC RICE............................................................................................................................................................................................... 69
BIOTECHNOLOGY......................................................................................................................................................................................... 70
OPPORTUNITIES AND CHALLENGES IN WATER-SAVING PRACTICES................................................................................................... 70
RICE-WHEAT CROP SYSTEMS IN WATER PRODUCTIVITY IN RELATION TO NEW RESOURCE CONSERVING TECHNOLOGIES...... 72
REDUCED TILLAGE.......................................................................................................................................................................................73
BED PLANTING SYSTEMS............................................................................................................................................................................ 73
MULTI USE OF LOW QUALITY WATER.......................................................................................................................................................75
NON-PUDDLING FOR RICE...........................................................................................................................................................................75
IMPORTANCE OF PARTICIPATORY TECHNOLOGY DEVELOPMENT....................................................................................................... 76
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III. BIO-INTENSIVE GARDENING AND OTHER COMPOSTING METHODS............................................................................................... 78
BIODIVERSITY-BASED FARMING SYSTEMS IN THE PHILIPPINES.......................................................................................................... 78
MAPPING THE INNOVATION SYSTEM OF CROP PROTECTION TECHNOLOGIES...................................................................................80
COMPOSTING................................................................................................................................................................................................ 81
VERMICOMPOSTING IN THE PHILIPPINES................................................................................................................................................84
INTERCROPPING PRODUCTION..................................................................................................................................................................85
VEGETABLE AGROFORESTRY SYSTEM...................................................................................................................................................... 85
INTEGRATION OF GREEN MANURES INTO THE CROP ROTATION......................................................................................................... 90
BACKYARD AND COMMUNITY - GARDENING IN THE URBAN PHILIPPINES......................................................................................... 91
CROP INTENSIFICATION VS. MORE DIVERSE PRODUCTION SYSTEMS.................................................................................................. 93
RESTORATIVE EFFECTS OF LEGUMES ON AGRICULTURAL SOIL......................................................................................................... 102
IV.
ALTERNATIVE PEST MANAGEMENT............................................................................................................................................... 106
PESTICIDAL PLANTS.................................................................................................................................................................................. 106
INVASIVE SPECIES......................................................................................................................................................................................108
A REVIEW OF IMPORTANT ALIEN INVASIVE SPECIES IN THE PHILIPPINES...................................................................................... 112
HERBICIDES................................................................................................................................................................................................ 118
MIXED CROPPING.......................................................................................................................................................................................125
MULCHING.................................................................................................................................................................................................. 127
WEEDS CONTROL....................................................................................................................................................................................... 130
PREDATORY BUGS......................................................................................................................................................................................137
STRATEGIES FOR ATTRACTING AND KEEPING BENEFICIAL INSECTS IN YOUR BACKYARD............................................................147
RICE WEED MANAGEMENT IN THE PHILIPPINES..................................................................................................................................148
PLAN CROPPING SYSTEMS TO MINIMIZE OPEN NICHES FOR WEEDS.................................................................................................149
NEEM........................................................................................................................................................................................................... 155
PERMACULTURE, CROPS AND WEEDS.....................................................................................................................................................156
BEATING THE WEEDS WITH INNOVATIVE COVER CULTIVATION.......................................................................................................166
CLASSICAL BIOLOGICAL CONTROL OF WEEDS.......................................................................................................................................171
WEED MANAGEMENT CHECKLIST FOR PERENNIAL AND OTHER WEED-SENSITIVE CROPS...........................................................175
V.
DIVERSIFIED AND INTEGRATED FARMING SYSTEMS..................................................................................................................180
EFFECT OF CASSAVA ON SOIL PRODUCTIVITY.......................................................................................................................................180
CROP/SOIL MANAGEMENT PRACTICES TO MAINTAIN OR IMPROVE SOIL PRODUCTIVITY.............................................................182
TRANSFER OF TECHNOLOGIES.................................................................................................................................................................184
FERTILIZING THE FIELDS WITH DUCKS..................................................................................................................................................185
INTEGRATED FARMING IS PROFITABLE................................................................................................................................................. 186
THE EXTRACTION OF MIMOSINE FROM IPIL-IPIL..................................................................................................................................187
INTEGRATED FISH FARMING....................................................................................................................................................................188
ACKNOWLEDGES........................................................................................................................................................................................193
BIBLIOGRAPHY........................................................................................................................................................................................... 194
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I.
AGRICULTURE THEN AND NOW - RURAL EXTENSION AND ORGANIC
AGRICULTURE
RURAL EXTENSION: AN INTRODUCTION
Agricultural extension work has a largely unrecorded, history. It is a significant force in
agricultural change, which has been created and recreated, adapted and developed the abilities of farm
people and to adopt more appropriate and often new practices and to adjust to changing conditions and
societal needs. The dissemination of relevant information and advice to farmers requires several
conditions for the initiation and organized development of agricultural extension work (Jones, G.E.
Garforth, C., 1997)
The information has to be assembled, systematized, based on either (or both) the accumulation
of experience or findings from research (however rudimentary).This information can be used to
educate professional agriculturists who may further enlarge or refine this knowledge or become active
promoters and disseminators of it. Therefore, an appropriate administrative or organizational structure
should exists by and within the dissemination activities to be established and conducted. A legislative
or some other official mandate for agricultural extension work is desirable and must occur. In addition,
the incidence of critical situations, such as famine, crop failure, soil exhaustion, or altered economic
conditions or relationships, may create an immediate cause for initiating the organization of extension
work.
Agricultural extension has now become recognised as an essential mechanism for delivering
information and advice as an "input" with a trend towards the privatization of the extension
organizations, often as parastatal or quasigovernmental agencies, with farmers being required to pay
for services which they had previously received free of charge. This trend is strong in the North, and
there are examples of it beginning in the South.
In much of the world, Organic Agriculture faces the challenge of keeping pace with rapidly
increasing population with few reserves of potentially cultivable land. Farmers will have to become
more efficient and specialized. Rural populations will undoubtedly be progressively better educated,
while their exposure to the mass media will continue to reduce their isolation and detachment from
information, ideas, and an awareness of their situation within a national and international context. The
continuing rapid development of telecommunications and computer-based information technology (IT)
is probably the biggest factor for change in extension, one which will facilitate and reinforce other
changes.
In the case of the Philippines islands its topography and agroecosystems demand more
independent, more client-oriented extension workers to commit into the dissemination of organic
agriculture technician and methods. Thus, this book tries to make a compendium of several on the
country methods on organic agriculture that are possible to be replicated in many other tropical and
Asian countries.
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ENVIRONMENTAL THREATS IN THE PHILIPPINES
The state of the Philippine environment is rapidly developing into a crisis situation. Through
time, various forms of environmental problems have mounted into unmanageable proportion. Among
these are massive deforestation, pervasive and health-impairing pollution, indiscriminate discharging
of mine tailing and other pollutants into the rivers and lakes, coastal and marine ecosystems
destruction, massive pesticide poisonings, degradation and erosion of agricultural lands, situation of
rivers and farmlands, salt water intrusion into aquifers, loss of biodiversity, and others (Pulhin, 2001).
The country’s declining environmental quality manifests itself in the frequent occurrence of
environmental disasters such as destructive floods and landslides during rainy season, prolonged
drought during dry season, and large scale poisoning and death of fishes and other aquatic resources,
to name a few. These in turn, persist to claim human lives and destroyed valuable infrastructures and
properties including poor people’s major sources of livelihood. Indeed, not unless the worsening
environmental situation of the country can be arrested, its adverse impacts will bite heavily on its
economy rendering elusive its pursuit towards sustainable development.
While adverse environmental change has negative repercussions on the entire citizenry, it has
its greatest impact on the lives of the poor. Poor people are often the most vulnerable in the society
because they are most exposed to a wide array of risks including those associated with environmental
disturbance. Their low income means they are less able to save and accumulate assets, which in turn
restricts their ability to deal with environmental crisis when it strikes.
That process give energies to increase to the rural population to emigrate in exodus from rural
to urban areas in the context of environmental and climate change pressures on farmers in co evolution
to fast environmental change. These social changes include the need for a more responsive policy and
practice on environmental management, massive public environmental education, and strengthening
support to research (Antón, J., Kimura, S., Lankoski L. & Cattaneo A., 2012).
The three main sets of environmental problems that beset the nation are pollution and waste
management-related problems associated with the "brown" environment; problems associated the with
"green" environment or natural resource degradation that threatens agricultural production, forests, and
biodiversity; and those linked with the "blue" environment that concerns water resources-related issues.
Land degradation persists with massive conversion of forest and grasslands into agricultural
lands and urban use. Despite increasing inputs like the application of chemical fertilizers and
pesticides, yield in lowland agricultural areas has been static and relatively low by Asian standards.
On the other hand, upland agriculture is even less productive and often leads to severe soil erosion due
to cultivation of sloping lands using standard lowland farming techniques.
Forest cover continues to decline through time. The principal direct causes of deforestation in
the country are logging, slash and burn farming, forest fires, and conversion of forestlands to
agricultural lands, human settlements and other development projects. While logging operations has
5
been drastically reduced, it remains a threat to deforestation. Conversion of uplands into agricultural
areas is also on the rise.
These adverse impacts include decline in socio-economic well-being including the lost
properties and lives, physical isolation, population displacement, and cultural disintegration including
the lost of indigenous knowledge systems that contribute to further environmental degradation.
Widespread poverty and limited livelihood opportunities have resulted to the influx of migrants to the
upland areas (Republic of the Philippines, 1997).
HAZARDS OF PESTICIDES
In the Philippines, the use of pesticides in rice and other production expanded rapidly and its
indiscriminate use is creating ecological imbalances that furthermore exacerbate, rather than alleviate,
a pest problem1. This situation of agrochemical abuse and other bad practices are forcing to farmers to
move towards more sustainable practices (Rola AC, & Pingali PL, 1993).
As a reaction to several researches developed by different agencies some policies banning the
use of some hazardous pesticides were enacted by the Fertilizer and Pesticide Authority (FPA) of the
Philippines in the early 1980s. In 1989, a pesticide policy package (PPP) was implemented, targeting:
The use of highly toxic insecticides in rice and veggies growing;
Regulatory policies and implementing guidelines on the importation, formulation, distribution,
sale, and use of pesticides;
The illegal smuggling of pesticides;
Regulation on the labeling and advertising of pesticides;
Hazard awareness, through an ago-medical training program;
Improved product stewardship, undertaken jointly by the pesticide industry and the
government.
The Philippines has currently no legislation, policies, guidelines or other forms of control that
specifically provides for the assessment, remediation or management of contaminated land. The
effective control of contaminated land and associated health and environmental hazards and risks
1
Pesticides are designed to kill, repel, attract, regulate or stop the growth of living organisms considered to be pests (United States
Environmental Protection Agency 2007). A pest is any type of living organism, e.g. mammals, birds, reptiles, fish, amphibians, mollusks,
insects, nematodes, weeds and microbes (bacteria and viruses), that competes with our food crops or space, spreads disease or acts as a
vector for disease and/or causes us discomfort. Pesticides include chemicals, biopesticides and biological agents (United States
Environmental Protection Agency 2007). High levels of agricultural productivity will be required to sustain the world population, given
current population growth rates. Between 1960 and 2000, the Green Revolution increased global food production by a factor of two to three
(Evenson and Gollin 2003 ). However, the approaches used to increase production damaged many ecosystems, rendering them more
vulnerable to pests. The control of these pests is essential if we are to maintain the high levels of productivity required to meet demand.
Organisms harmful to humans, their environment and production can be controlled in many different ways. Pesticides are one of the most
widely used and effective tools for this purpose.
6
relies on use of other legislation such as RA 6969 and Presidential Decree 1586 namely the Philippine
Environmental Impact Assessment regulation. Existing controls on toxic chemical and hazardous
wastes, however, have some effect on limiting the occurrence of land contamination, while programs
for monitoring and controlling effects on marine and fresh waters or groundwater also lead to
management of land-based contamination source.
Despite all that, in the Philippines, nationwide IPM-FFS activities, more formally known as
the KASAKALIKASAN program, were first instituted as a five-year program (1993-1997) under the
Department of Agriculture. Only limited program resources come from local governments, the private
sector and some NGO’s. The central government’s goal is to increase support from these latter sources
because farmer coverage by the national effort is still limited (Bordey F. H., 2015).
IMPACT OF PESTICIDES ON FARMER'S HEALTH AND THE ENVIRONMENT
Pesticides continue to be a significant and growing component of modern agriculture
technology. Indiscriminate pesticide use can result in one or more of the following: (1) health
impairment due to direct or indirect exposure to hazardous chemicals; (2) contamination of ground and
surface waters through runoff and seepage; (3) the transmittal of pesticide residues through the food
chain to the farm family and urban consumers; (4) an increase in the resistance of pest populations to
pesticides, thereby reducing their efficacy and consequently causing pest outbreaks; (5) the reduction
of beneficial insects like parasites and predators, thereby reducing the effectiveness of pest control
strategies that attempt to minimize pesticide use; and (6) the reduction in the populations of
microorganisms in the paddy soil and water that help sustain soil fertility while lowering chemical
fertilizer use. The incidence and magnitude of each of these effects depend on the types of chemicals,
frequency and quantities applied, and their persistence (Pingali, PL, Hossain, M & Gerpacio RV,
1997).
Where any of the above externalities are significant, the farmer’s private costs of pesticide use
are lower than the social costs of pesticide use. This would be so, since farmer’s private pest control
decisions may not consider the damage to the environment and to health (due to a lack of information
or otherwise). Knowing the incidence and magnitude of these social costs is important for identifying
the true returns to promoting alternative strategies for pest control and for pesticide regulatory policy.
In Asian rice systems, pesticide use is small in terms of dosages and number of applications,
and the chemicals used degrade more rapidly in tropical flooded conditions than in the temperate
upland conditions. While the chemicals used tend to degrade rapidly, they are, however, extremely
toxic to humans, and exposure even at low levels tends to cause both acute and chronic health
problems (Pingali, PL, & Rosegrant NW, 1995)
7
Many pesticides commonly sold in Asia, extremely hazardous category I and II chemicals, are
either banned or severely restricted for use in the developed world even when used with high levels of
protection. In Asia, these chemicals are used with minimal protection, and the opportunities for
increasing farmer safety are small. Pesticide regulation could help reduce the health costs borne by
farmers by targeting the most hazardous and least productive pesticides. Finally, this document
encourages to move towards high rates of return to research on non chemical pest control methods,
such as varietal resistance to pests that can be embodied in seeds, or the use of natural enemies and
other biological controls.
In the specific case of rice production it accounts for about half the total insecticides, over 80
percent of the herbicides, and 4 percent of the fungicides sold in the Philippines. Molluscicides have
also been used in small quantities since 1987 to control the growing snail infestation. Relative to
heavy users such as South Korea and Japan, the total amount of pesticides used in the Philippines is
small (Isman, M.B., 2006).
However, unsafe pesticide storage, handling, and disposal practices, subject the farmer to high
levels of health hazards and contaminate the paddy ecosystem. Safe spray equipment and protective
clothing, suitable for tropical conditions, are not available for Philippine rice farmers. Farmers also
forage the rice paddies for food, such as fish and frogs, and feed, such as aquatic plants and rice straw,
that could be contaminated by pesticides (Pingali, PL, Rosegrant NW, 1995).
Farmers often lack accurate knowledge about pests and their control, hence under dosing and
frequent applications are generally observed. Current pesticide pricing and regulatory structure plus
inadequate storage, unsafe handling practices, short reentry intervals, and inefficient sprayer
maintenance taken together provide an environment of greater accessibility or exposure to chemicals
not only by the farmer applicator but by the farming household as well. Training and information
campaigns on proper pesticide management could reduce the social costs of pesticide use, but these
are too few in number and inadequate in content.
With the advent of rice varieties that are resistant to a wide variety of insect and disease
pressures, the importance of pesticides for reducing yield variability has declined. Rola and Pingali
(1993)
have shown that the yield gains through insecticide application are modest when using
resistant varieties, and that natural control or the “do nothing” option is the most profitable pest
control strategy under normal circumstances. The release of resistant varieties, however, was not
accompanied by supporting information campaigns on the reduced need for insecticides. Consequently,
continued high and injudicious insecticide applications lead to the frequent breakdown in varietal
resistance.
Rice paddies are home to an intricate food chain composed of vertebrate and invertebrate
organisms. The dominant group of vertebrates are fish, frogs, and rats. The invertebrates, in turn,
range from macro- to microorganisms: crustaceans (crabs, crayfish, and shrimp), micro crustaceans
8
(these are best described as small crabs, ostracods, copepods, and cladocerans), aquatic insects and
insect larvae, molluscs (snails), annelids (worms), microflora (algae), and microfauna (bacteria).
Maintaining a balance among these groups of organisms is essential both for human nutrition
and for sustaining soil fertility. Nutrient recycling in the paddy soils occurs essentially through inter
dependencies of the micro and macro organisms in the paddy soil and water complex habitats.
Research on nitrogen uptake by the rice plant has shown that most of the nitrogen absorbed by
the plant originates from the soil. Only a small fraction of the nitrogen in the soil is available to the
plant, and most of this available nitrogen originates from the soil’s microbial biomass (Watanabe, De
Datta, and Roger, 1988). Crop residues, algae, aquatic plants, tubificid worms, and other soil
organisms contribute to the replenishment of microbial biomass. There is a concern that enhanced
pesticide use might alter the soil microflora and microfauna responsible for maintaining soil fertility.
The impact of pesticides on pest populations is quite well understood for the Philippines for a
survey of the literature and evidence). The impact of pesticides on predator populations is less well
understood but is the subject of current inquiry at IRRI. The impact of pesticides on predator
populations has substantial implications for pest control strategies that attempt to minimize pesticide
use, such as integrated pest management. Applying pesticides continuously in the crop season or on
schedule during the growing season (prophylactic application)-disrupts the pest-predator balance.
Heong (1991) has shown that the predominant reliance on chemical control often leads to pest
resurgence and frequent large-scale infestations.
Some researches show that for flooded rice, pesticides applied at recommended rates and
intervals do not persist beyond the crop growing period, either in soil, in paddy water, or on the plant
and rice grains. The problem, however, is that during the short period that they persist in the paddy
environment they can have adverse effects on aquatic vertebrate and invertebrate organisms and on
farm labor that enters the field to conduct other agricultural operations.
With respect to soil and aquatic microflora and fauna, existing evidence seems to indicate that
pesticides have only a temporary and transient effect. For aquatic vertebrates, the absolute numbers
decline rapidly with pesticide use, although the level of detectable residues in the surviving
populations is generally small. The important point here is that pesticide-using farmers trade off a
higher quantity of protein supply from the paddy for a perceived increase in rice output. Deliberate
interventions to increase protein supply from the paddy, through rice-fish farming for instance, would
only be successful with advances in pest management technology that minimizes the above trade off.
The ability of rural households, particularly the rural poor, to forage for protein food is limited
by the extent that pesticides contaminate the canals surrounding the paddy and affect the quantity and
quality of aquatic vertebrates. Similarly, seasonal groundwater contamination could have a significant
impact on farm household as well as on other rural household health.
9
The findings of this study establish, for the case of irrigated rice in the Philippines, a
consistent pattern showing that pesticide use has an adverse impact on human health and that
impairment of health reduces farmer productivity. Eye, skin, pulmonary, and neurology problems are
significantly associated with long-term pesticide exposure. The majority of the pesticides that might be
linked to these impairments (the highly hazardous category I and II chemicals) are commonly
available in the Philippines but are banned or severely restricted in the developed world.
Taxes on pesticides can be used to reduce farmers’ health risks and environmental externalities.
For instance, if governments tax the highly toxic category I and II chemicals heavily enough, farmers
may switch to the less hazardous category III and IV chemicals. More discretion should also be used
in importing and licensing agrochemical s. Judicious pest management is possible only when
policymakers and farmers discriminate in their choice of pest control methods and chemicals (Lu J. L.,
2009).
Emphasis on agricultural production using modem techniques has focused attention on the
problem of yield losses due to pests and the need for adequate protection of the crop. Pesticide
application is currently the most widely practiced method of pest control in rice and rice-based
cropping systems. Because of their toxic nature there is a general concern with the potential hazards of
pesticides to humans and the environment (Balisacan, A.M., Sebastian, L.S. and Associates., 2006).
The fate of pesticides applied in agricultural ecosystems is governed by the transfer and
degradation processes and their interactions. Transfer is a physical process in which the pesticide
molecules remain intact; it includes adsorption, runoff, percolation, volatilization and absorption by
crop plants or animals. Degradation is a chemical process in which pesticide molecules are split; it
includes photodecomposition, microbiological decomposition, chemical decomposition, and plant
detoxification. Transfer and degradation determine pesticide persistence or retention, its efficacy for
pest control, as well as its potential for contamination of the soil and water resources.
Growing evidence indicates that pesticides are present in food grown on the land in surface
bodies of water and in the atmosphere. Research has established the toxic effects of some pesticides on
fish and other aquatic animals, on birds and other wildlife, and on human health. There is therefore a
growing interest in understanding the processes relevant to the transport, transformation, and retention
behaviors of pesticides used in agricultural production systems (Aktar, W., Sengupta, D. &
Chowdhury, A., 2009).
In most rice-growing countries, insecticides are the dominant class of pesticides used (Van der
Valk and Koeman, 1988). In the Philippines, for example, 55 to 60 percent of the pesticides used
before 1980 were insecticides, 20 to 25 percent fungicides, and 5 to 16 percent herbicides. However,
herbicide use is increasing rapidly due to the escalating costs of labor in many areas (Moody, 1990).
10
Molluscicides have recently been introduced in some rice-growing regions in Asia where golden snails
(Pomacea canaliculata) have become a threat to rice seedlings.
Pesticides may be introduced directly into the environment in a liquid phase, as a dispersion or
solution, or in the solid phase-as a powder, micro capsule, or granule. Sprays are directed to the
foliage or the soil. Solids are applied directly to the soil surface or to foliage. Pesticides may be
incorporated directly into the soil, usually at the top few millimeters to exert a biological effect.
Pesticides may also enter the environment through accidental spill or waste disposal (Himel, Loats,
and Bailey, 1990).
Environmental entry and transport processes start immediately after the pesticide has been
applied. Irrigation or rainfall may modify the relative importance of the various components of these
processes in determining the fate of the applied pesticide. Environmental sinks for pesticides include
chemical, photochemical, and biological transformation, volatilization losses, erosion and runoff,
leaching, and harvest removal and storage.
The environmental pollution from pesticides is caused mainly by the physical processes of
pesticide transfer. Several of these processes may be active simultaneously. Soil is contaminated by
pesticide adsorption, surface water is contaminated by pesticides moved through runoff, groundwater
quality is deteriorated by pesticides reaching the water table through leaching and deep percolation,
and the atmosphere is polluted by the volatilization of pesticides. Through absorption by crops or
aquatic animals, pesticide residues can get into human beings and animals that depend on them for
food. Pesticide degradation processes decrease the severity of its concentrations in soil and water
systems.
Runoff in surface water bodies is the principal route for pesticides from rice fields to rivers,
lakes, and marine ecosystems. Accumulation of pesticides in surface water bodies can have farreaching consequences for domestic water supply and aquatic organisms. Pesticide contamination of
surface water bodies can be assessed by monitoring residue levels in aquatic food webs.
Groundwater contamination by agricultural chemicals is a major environmental pollution issue.
In recent years, a number of organic contaminants have been detected in groundwater samples.
However, no systematic studies have been conducted for detection of groundwater contamination in
rice-growing areas of Asia, where multiple rice cropping with associated intensive pesticide use has
been commonly practiced for many years. Groundwater contamination is probably higher in such
areas than in more traditional one crop per year areas, particularly when the water table is shallow and
the aquifer is overlain by light-textured soils.
The results of the health assessment indicate that farmers and agricultural workers face chronic
health effects due to prolonged exposure to pesticides. Eye, dermal, pulmonary, neurology, and kidney
problems were found to be significantly associated with long-term pesticide exposure. The
11
relationship between these symptoms and pesticide use are discussed below. One or more of these
symptoms could lead to lower productivity due to the farmer’s being absent from work during
treatment and recuperation or to impaired capacity of the farmer to do a full load of work. The
following pesticide-related health abnormalities could be addressed:
•
Eye Problems: Pesticides such as 2,4-D and acetamides are known eye irritants.Chronic
irritation of the eye could lead to the formation of pterygium, a vascular membrane over the
cornea, which can cause diminished vision.
•
Dermal Problems: The skin is the main biomode for entry of pesticides. Dermal contamination
occurs during application as well as during mixing and handling of concentrated formulations.
The risk of dermal contamination is greater with the backpack sprayer typically used in the
Philippines as compared to a spinning disc applicator or an electrodyne sprayer. Dermal
absorption of the chemicals is enhanced by perspiration and the high temperatures typical of
the tropical lowland conditions in the Philippines.
•
Respiratory Problems: The lung is an important biomode of entry for airborne pollutants.
There is an immediate intimate contact between the lung alveolar and the pesticide aerosol.
The lungs are an important site for the binding or metabolism of organophosphate compounds.
•
Neurology Problems: Organophosphate compounds and 2,4-D are known neurotoxicants.
Both have been implicated as causative agents for polyneuropathy, a syndrome characterized
by paralysis or weakness of muscles of the arms and legs usually accompanied by a “glove
and stocking” distribution of sensory loss and diminished deep tendon reflexes. Five percent
of the Laguna sample and 11 percent of the Nueva Ecija sample were found to exhibit
symptoms of polyneuropathy.
•
Kidney Problems: The kidneys help to ensure the efficient functioning of body cells through a
number of mechanisms: regulation of extra cellular fluid volume, control of electrolytes and
acid-base balance; excretion of toxic and waste products, and conservation of essential
substances.
Although the above illnesses can be directly related to pesticides, pesticides also cause other
nonspecific illnesses and lead to the lower health status of the farmer. In order to relate farmer health
to pesticide exposure, a general indicator of health impairment was constructed that is comparable
across illnesses. Medical examinations provided for each respondent an assessment of the ailments he
or she experienced and the seriousness of these ailments. These assessments provided the basis for the
estimation of the costs of treatment and recuperation (Andersson H, Tago D, & Treich N., 2014).
12
STANDARDS FOR ORGANIC CROP PRODUCTION
These standards have been prepared for the purpose of providing an agreed approach to the
requirements which underpin production of, and the labelling and claims for, organically produced
foods. The aims of these standards are (Nick Feinstein, 2013):
· To protect consumers against deception and fraud in the market place and unsubstantiated product
claims;
· To protect producers of organic produce against misrepresentation of other agricultural produce as
being organic;
· To ensure that all stages of production, preparation, storage, transport and marketing are subject to an
internal control scheme (of organization where the operator is member) and comply with these
standards;
· To harmonize provisions for the production, verification scheme, identification and labelling have
organically grown produce;
· To maintain and enhance organic agricultural systems in Cambodia so as to contribute to local and
global preservation.
These standards set out the principles of organic crop production at farm, preparation, storage,
transport, labelling and marketing stages, and provides an indication of accepted permitted inputs for
soil fertilizing, conditioning, soil improvement, and plant pest and disease control. For labelling
purposes, the use of terms inferring that organic production methods have been used are restricted to
products derived from operators under the supervision of a member organisation (e.g. organic
farmer/grower association)
Organic agriculture is one among the broad spectrum of methodologies which are supportive
of the environment. Organic production systems are based on specific and precise principles of
production which aim at achieving optimal agro-ecosystems which are socially, ecologically and
economically sustainable. Requirements for organically produced foods differ from those for other
agricultural products in that production procedures are an intrinsic part of the identification and
labelling of, and claim for, such products.
“Organic” is a Labelling term that denotes products that have been produced in accordance
with organic production standards and verified by an organic growers associations. Organic
agriculture is based on minimizing the use of external inputs, avoiding the use of synthetic fertilizers
and pesticides. Organic agriculture practices cannot ensure that products are completely free of
residues, due to general environmental pollution.
However, methods are used to minimize pollution of air, soil and water. Organic food handlers,
processors and retailers adhere to standards to maintain the integrity of organic agriculture products.
13
The primary goal of organic agriculture is to optimize the health and productivity of interdependent
communities of soil life, plants, animals and people.
Organic agriculture means holistic production management systems which promote and
enhance agro-ecosystem health, including biodiversity, biological cycles, and soil biological activity.
This is accomplished by using, where possible, cultural, biological and mechanical methods, as
opposed to using synthetic materials, to fulfil any specific function within the system. Management
practices may differ to achieve locally adapted systems.The concept of close contact between the
consumer and the producer is a long established practice and today is used in low income countries for
supplying the domestic markets. For this type of markets and especially in the case of small-holder
production, alternative control schemes have been developed.
These standards describe the requirements for organic production. It covers plant (including
mushroom) production, collection of wild products and also the processing and labelling of products
derived from these activities. This standard provides a mechanism to define the expectations for
organic production. When complied with, it also enables producers to label their products as organic.
The standard does not cover procedures for verification, such as inspection or certification of products.
The development of this standard is guided by the following objectives established for organic
farming;
· Employing long-term, ecological, systems-based organic management.
· Assuring long-term, biologically-based soil fertility.
· Avoiding/minimizing synthetic inputs at all stages of the organic product chain and
expo- sure of people and the environment to persistent, potentially harmful chemicals.
· Minimizing pollution and degradation of the production/processing unit and
surrounding environment from production/processing activities.
· Excluding certain unproven, unnatural and harmful technologies from the system.
· Avoiding pollution from surrounding environment.
· Maintaining organic integrity throughout the supply chain.
· Providing organic identity in the supply chain.
Organic farming systems and standards are continually evolving in response to changing
knowledge, production and market conditions. It is anticipated that in the future the scope of this
standard may be broadened to include – livestock, aquaculture, textile and other types of production –
and as well include additional requirements to enhance attainment of the above and possibly additional
objectives established for organic farming (Uphoff, N., 2013)
Organic production and processing systems are based on the use of natural, biological,
renewable, and regenerative resources. Organic agriculture maintains soil fertility primarily through
the recycling of organic matter. Nutrient availability is primarily dependent on the activity of soil
organisms. Pests, diseases, and weeds are managed primarily through cultural practices. Organic foods
14
and other products are made from organically produced ingredients that are processed primarily by
biological, mechanical, and physical means.These benefits include:
Ecological Sustainability
· Recycling nutrients instead of applying external inputs.
· Preventing the chemical pollution of soil, water and air.
· Promotion of biological diversity.
· Improving soil fertility and the build-up of humus.
· Preventing soil erosion and compaction.
· Promoting the use of renewable energies.
Social Sustainability
· Supporting sufficient production for subsistence and income earning for small farmers.
· Providing safe and healthy food.
· Supporting the adoption of good working conditions.
· Building on local knowledge and traditions.
Economic Sustainability
· Helping farmers achieve satisfactory and reliable yields.
· Providing a lower reliance on and associated cost for external inputs.
· Promoting crop diversification to improve income security.
· Promoting product value addition through quality improvement and on-farm
processing.
· Promoting the adoption of efficient farming systems to improve overall profitability
and competitiveness.
GENERAL REQUIREMENTS FOR ORGANIC PRODUCTION AND PROCESSING
Ecosystem Management
All farming systems ensure the long-term management and resilience of an organic farm
holding by respecting, maintaining, improving and completing ecological cycles and the quality of
ecosystems and the landscape. Organic management maintains and / or enhances biodiversity on the
farm holding, in crop and where applicable non-crop habitats. Examples of biodiversity enhancement
strategies include the use of crop rotation, multiple cropping, green manuring, hedgerow plantings and
border crops. Organic management does not undertake any actions that create any negative impacts in
officially recognized high conservation value and heritage areas- such as forests wildlife protection
areas and watershed areas.
15
Organic production systems conserve and improve the soil, maintain both ground and surface
water quality and use water efficiently and responsibly. Risks of environmental pollution are identified
and minimized.
Organic crop production systems conserve or improve soil physical, chemical and biological
properties including; organic matter, fertility and soil biodiversity. They enhance soil primarily by
employing cultural management practices, incorporating manures and other biodegradable inputs, and/
or by nitrogen fixation from plants (Forrester D.I., 2004).
Soil fertility management employs measures to recycle organic materials within the production
system where possible such as green manuring and composting. Land clearing and preparation by
burning vegetation is prohibited except where it is part of an established and well managed traditional
management practice e.g. slash and burn shifting cultivation where it is to be restricted to a minimum.
These systems employ measures to prevent land degradation, such as erosion, salinization and
other related risks to soil loss and degradation. Organic management ensures that water resources are
used efficiently to meet farm production requirements with strategies established to optimize water use
and prevent wastage. Organic management prevents pollution of the environment and preserves the
quality of land and water.
Organic management strictly limits the use of synthetic inputs at all stages of the organic
production/supply chain and exposure of people and the environment to persistent, potentially harmful
chemicals. It minimizes pollution and degradation of the production/processing unit and surrounding
environment from production/processing activities. It also excludes certain unproven, unnatural and
harmful technologies from the system.
Organic management takes precautionary measures to avoid contamination that could affect
the organic integrity of the supply chain. Precautionary measures may include barriers/buffer zones in
production, cleaning of farm equipment, use of dedicated facilities and equipment and cleaning in
processing. Organic management actively addresses risks of contamination. Where there is reasonable
suspicion of contamination, efforts shall be made to identify and address the source of contamination.
Organic management systems do not use genetically modified organisms (GMO) or their derivatives,
in all stages of organic production and processing.
Organic management systems restrict the use of non-bio-degradable coverings and mulches.
The harvesting of products from wild or common land areas is undertaken sustainability, does not use
prohibited inputs or practices and ensures products are not contaminated. Organic wild harvest
management ensures that harvesting does not exceed the sustainable yield of the harvested species or
otherwise threaten the local ecosystem. Organic operators harvest products only from within the
boundaries of the clearly defined wild harvest area as at an appropriate distance from conventional
farming, pollution and other potential sources of contamination.
16
Conversion Requirements
Conversion to organic production requires a period of time in which healthy soils, sustainable
ecosystems are established and contaminants reduced before it can achieve certified organic status.
There shall be a period of at least 12 months organic management for annuals and 18 months for
perennials that meets all the requirements of these standards before the resulting product can be
considered organic. The conversion period can be extended based on the identification and evaluation
of relevant issues and risks. An exemption to this requirement may be approved where there is a
verifiable record of the unbroken use of traditional agriculture practices with no use of non-permitted
inputs or activities. The start of the conversion period shall be calculated from the date of the
documented start of organic management. The integrity of an organic farm unit is not compromised by
the activities and management of non- organic operations undertaken on the same farm.Organic
management completely and clearly separates the non-organic and organic parts and products of
holdings with split or parallel production, e.g. through physical barriers; management practices such as
the production of different varieties or the timing of harvest; storage of inputs and products (FAO,
2001).
Maintenance of Organic Management
Organic management does not rely upon switching back and forth between organic and
conventional management. Exceptions to this may only be made in cases where compelling reasons to
cease organic management on the certified organic land are present and in these cases conversion
requirements apply.
Crop Production Management Systems
Appropriate crops and varieties are grown to suit local conditions. The organic integrity of
crops is maintained in production. Operators are encouraged to preserve the plant genetic integrity of
varieties and traditional ecotypes. As an example the use of locally sourced or native varieties is
encouraged while the use of GMO varieties is prohibited. Organic crop production uses seed and
planting materials that are of organic quality unless such seed and materials are unavailable. Organic
crop production systems use untreated seeds and planting materials whenever available. If treated, they
are treated only with substances that are listed unless treatment with other substances is required or
unless seed and planting material not treated with these other substances is unavailable. In these
situations any prohibited chemical treatment shall be removed from the seeds or planting materials
before use. Exemptions are limited in time or subject to review.
Diversity in Crop Production
The selection of crop species and varieties is based on an understanding of their adaptation to
local conditions, pests and diseases and the broader ecological relationships present in healthy farming
17
systems. Organic crop production systems produce terrestrial crops in soil based systems. Organic
crop production includes the use of diverse plantings as an integral part of the farm management
system. For perennial crops, this includes the use of plant-based ground cover. For annual crops, this
includes the use of crop rotation practices, cover crops (green manures), integrated crop management,
inter cropping or other diverse plant production with comparable achievements.
Soil Fertility and Fertilization
Soil fertility management nourishes plants primarily through the soil ecosystem and achieves
nutrient balance. Organic soil fertility management uses only naturally occurring mineral fertilizers
and only as a supplement to biologically-based fertility methods such as green manures and compost.
Organic soil fertility management does not use:
• Synthetic fertilizers;
• Fertilizers made soluble by chemical methods, e.g. super phosphates.
Organic soil fertility management does not use human excrement on leafy, tuber or root crops.
Where it is used in other crops it will not come into contact with the edible parts of a crop and
measures are established to protect humans from pathogens for example through composting or
fermentation.
Pest, Disease, Weed and Growth Management
Crop production management systems promote and sustain the health of crops while
maintaining productivity and the integrity of the Agra-ecosystems. Organic crop production
management employs interrelated positive processes and mechanisms for the management of pests,
diseases, and weeds. These include but are not limited to site and crop adapted fertility management
and soil tillage, crop cultural practices, choice of appropriate varieties, enhancement of functional
biodiversity e.g. planting host plants for beneficial insects, mulching to control weeds. In case
additional measures are required, thermal controls and the use of crop protectants and growth
regulators are permitted (Abouziena, H.F, and Hagaag, & W.M., 2016).
Post Harvest Management
On farm post harvest management maintains the organic integrity of organic products. Onfarm post harvest management takes measures to prevent contamination and co mingling of organic
products with non-organic products in processing, handling, packaging, storage and transport; for
example in the threshing, peeling, hulling, cleaning, cooling, cutting, drying and packing of products.
18
Processing and Handling
Processing and handling management systems maintain the organic integrity of organic
products. Organic processing management takes measures to prevent contamination and co mingling
of organic products with non-organic products in processing, handling, packaging, storage and
transport. For example – the transportation of organic and non-organic products can only occur if
adequate measures are in place to prevent mixing or contamination such as the products having
different label ling and separate handling practices.
Ingredients
Organic processed products are made from organic ingredients. Organic processing uses only
organic ingredients except for when they are not available and subject to the labelling requirements in
section 5. The same ingredient in a product shall not be derived from both an organic and a nonorganic source. Organic processing only uses minerals (including trace elements), vitamins, essential
fatty, amino acids, and other isolated nutrients when their use is legally required or strongly
recommended by the competent authority, in the food products in which they are incorporated.
Processing Methods
Organic food is processed by biological, mechanical or physical processing techniques. For food and
feed production, organic processing uses only processing methods that are biological, mechanical and
physical in nature such as hulling, milling, fermentation, grinding, pressing and dehydration. Organic
processing uses only additives, processing aids, other substances that modify organic products and
solvents used for extraction. Organic processing does not use irradiation (ionizing radiation)
technologies. Filtration techniques used in organic processing do not chemically react with or modify
the product at the molecular level.
Pest and Disease Control
During processing, storage and handling – organic products are protected from pests and
diseases without compromising the organic integrity of the product. Organic processing management
systems control pests according to a hierarchy of practices starting with prevention, and then physical,
mechanical, biological methods and substances.. Pest and disease control examples include the use of
physical barriers, sound, ultra-sound, light and UV-light, traps (including pheromone traps),
temperature control, controlled atmosphere and diatomaceous earth. Where these practices are not
effective, and other substances are used, they do not come into contact with the organic product.
Packaging
Packaging and storage/transportation containers do not contaminate the organic product they
contain. The packaging, storage and transportation containers used for organic products do not
19
contaminate the organic product. For example – packaging materials or storage containers that contain
a synthetic fungicide, preservative or fumigant are prohibited as is the use of reused bags or containers
that have been in contact with any substance likely to compromise the organic integrity of a product or
ingredient placed in those containers.
Cleaning, Disinfecting and Sanitizing of Food Processing Facilities
Cleaning, disinfecting and sanitizing of food processing facilities does not contaminate
organic products. Organic management employs only those systems for cleaning and disinfecting
surfaces, machinery and processing facilities that prevent contamination of the organic product.
Organic processing restricts disinfecting and sanitizing substances that may come in contact with
organic products to water and substances. In cases where these substances are ineffective and others
must be used, these other substances must not come into contact with any organic products.
Labelling
Labelling clearly identifies organic products and provides relevant information for consumers
to make informed, conscious choices and to avoid misleading them. Labelling fully discloses
ingredients in the order of their weight percentages and whether or not they are organic. As an
exemption - if herbs and/or spices constitute less than 2 % of the total weight of the product, they may
be listed as “spices” or “herbs”. Labelling identifies the entity legally responsible for the product and
the body that assures conformity to the applicable organic standard. Claims that processed products
are “organic” are made only if the product contains at least 95% organic ingredients (by weight for
solids or by volume for liquids- excluding water and salt). The non-organic ingredients shall not be
genetically modified, irradiated or treated with processing aids.
Claims that processed products are “made with organic ingredients” or similar terms are made
only if the product contains at least 70% organic ingredients (by weight for solids or by volume for
liquids - excluding water and salt). Labelling does not make “organic” or “made with organic
ingredients” or similar terms, or make any organic certification claims on products with less than 70%
organic ingredients (by weight for solids or by volume for liquids- excluding water and salt), although
“organic” may be used to characterize ingredients on the list of ingredients.)
Labelling clearly distinguishes in-conversion products or similar terms from organic products.
Labelling ensure that products labelling ed as “organic” or “in-conversion”, or an equivalent term (e.g.
biologic or ecological), comply with the applicable organic standards.
Appendices
These appendices detail approved inputs that can be used in the production and processing of
organic food (GOMA, 2012).
20
These standards set out the principles of chemical free crop production at farm, preparation,
storage, transport, labelling and marketing stages, and provides an indication of accepted permitted
inputs for soil fertilizing and conditioning, plant pest and disease control. For labelling purposes, the
use of terms inferring that chemical-free production methods have been used are restricted to products
derived from operators under the supervision of a member organization (e.g. organic farmer/grower
association).
Chemical free agriculture is one among the broad spectrum of methodologies which are
supportive to the environment. Requirements for chemical free produced foods differ from those for
other agricultural products in that production procedures are an intrinsic part of the identification and
labelling of, and claim for, such products.
“Chemical free” is a labelling term that denotes products that have been produced in
accordance with chemical free production standards and verified by a member organisation. Chemical
free agriculture does not allow the use of agro-chemicals in the whole farm or a specific part of the
farm. Chemical free agriculture practices cannot ensure that products are completely free of residues,
due to soil pollution of previous production and due to general environmental pollution. However,
methods are used to minimize pollution of air, soil and water. Chemical free produced food handlers,
processors and retailers adhere to standards to maintain the integrity of chemical free agricultural
products. The primary goal of chemical free agriculture is to minimize residue contamination in food
and to reduce pollution of the environment.
The concept of close contact between the consumer and the producer is a long established
practice and today is used in low-income countries for supplying the domestic markets. For this type
of markets and especially in the case of small-holder production alternative control schemes have been
developed.
These standards apply to the following products which carry, or are intended to carry,
descriptive labelling referring to chemical free production methods:
a) unprocessed products from plants,
b) processed agricultural crops intended for human consumption derived from (a) above.
A product will be regarded as bearing indications referring to chemical free production
methods where, in the labelling or claims, including advertising material or commercial documents,
the product, or its ingredients, are described by the term "chemical free". These standards apply
without prejudice to other standards governing the production, preparation, marketing, labelling and
inspection of the products specified. Products and by-products treated with ionisation radiation for
post harvest treatment are not permitted under this standard definitions:
•
Agro-chemical means chemical used in agricultural production (as an herbicide or an
insecticide.)
21
•
Chemical-free agriculture means agricultural production system, which does not allow
the use of fertilizers and pesticides.
•
Fertilizer means synthetic chemical substance or mixture used to promote plant
growth.
•
Genetically engineered/modified organism means the following provisional definition
provided for genetically/modified organisms. Genetically engineered/modified
organisms, and products thereof, are produced through techniques in which the genetic
material has been altered in a way that does not occur naturally by mating and/or
natural recombination or through traditional breeding.
•
Inspection means the examination of food or systems for control of food, raw
materials, processing, and distribution, in order to verify that they conform to
requirements. For chemical free food, inspection includes the examination of the
production and processing system.
•
An Internal Control System (ICS) is the part of a documented quality assurance
system that allows an external certification body to delegate the periodical inspection
of individual group members to an identified body or unit within the certified operator.
This means that the third party certification bodies only have to inspect the wellfunctioning of the system, as well as to perform a few spot-check re-inspections of
individual smallholders
•
Labelling means any written, printed or graphic matter that is present on the label,
accompanies the food, or is displayed near the food, including that for the purpose of
promoting its sale or disposal.
•
Marketing means holding for sale or displaying for sale, offering for sale, selling,
delivering or placing on the market in any other form.
•
Operator means any person who produces, prepares or trades chemical-free products
as referred to in Section 1.1, or who markets such products.
•
Pesticide means any toxic substance used to kill animals or plants that damage crops
or ornamental plants or that are hazardous to the health of domestic animals or
humans. All
pesticides act by interfering with the target species' normal
metabolism. They are often classified by the type of organism they are intended to
control (e.g., insecticide, herbicide,
fungicide). Some inadvertently affect other
organisms in the environment, either directly by their toxic effects or via elimination
of the target organism.
•
Pesticide residue means pesticides, including active substances, metabolites and/or
breakdown or reaction products of active substances currently or formerly used in
plant protection products that may remain on or in food after they are applied to food
crops.
22
•
Plant protection product means any substance intended for preventing, destroying,
attracting, repelling, or controlling any pest or disease including unwanted species of
plants or animals during the production, storage, transport, distribution and processing
of food, agricultural commodities, or animal feeds.
•
Preparation means post harvest handling, processing, and packaging of agricultural
products and also alterations made to the labelling concerning the presentation of the
organic production method.
•
Production means the operations undertaken to supply agricultural products in the
state in which they occur on the farm, including initial packaging and labelling of the
product.
•
Agricultural product/product of agricultural origin means any product or commodity,
raw or processed, that is marketed for human consumption (excluding water, salt and
additives) or animal feed.
The labelling and claims of a product may refer to chemical free production methods only
where:
1. such indications show clearly that they relate to a method of agricultural production; and
2. the products were produced, handled and processed according to this Standards.
The labelling should refer to this standards or the chemical free producer association where the
farmer is member. Starting with the production cycle, the use of all kind of agro-chemicals is not
permitted in the whole farm (or specific sections of the farm), if the crop is intended to be labelled as
chemical-free. The fertilization of the crop can be done by:
a) incorporation in the soil of organic material, composted or not. Farmyard manure from
intensive chicken farms is not allowed. Substances can be applied in the case sufficient organic matter
and manures are not available.
b) cultivation of legumes, green manures or deep-rooting plants in an appropriate mufti-annual
rotation programme;
c) for compost activation, appropriate micro-organisms or plant-based preparations may be
used;
Pests, diseases and weeds should be controlled by any one, or a combination, of the following
measures:
a. choice of appropriate species and varieties;
b. appropriate rotation programs;
c. mechanical cultivation,
23
d. protection of natural enemies of pests through provision of favourable habitat, such as hedges and
nesting sites, ecological buffer zones which maintain the original vegetation to house pest predators;
e. diversified ecosystems; for example, buffer zones to counteract erosion, agroforestry, rotating crops,
etc.
f. natural enemies including release of predators and parasites;
g. bio dynamic preparations from stone meal, farmyard manure or plants;
h. mulching and mowing;
i. grazing of animals;
j. mechanical controls such as traps, barriers, light and sound;
k. steam sterilization when proper rotation of soil renewal cannot take place;and
l. water management.
The production standards must be applied with the start of the new cropping cycle onward. For
annual crops, the growing season starts with the land preparation activities for the respective crop. For
perennial crops, the chemical-free management must commence at least immediately after the
previous harvest. In addition, the operator must assure that herbicides and insecticides of the Class IA
+ IB and Class II (WHO classification) have not been applied during the six months prior to the
conversion of the area intended for chemical-free production.
Before products from a farm can be certified as chemical-free, internal peer visits/inspections
shall have been carried out. The operator is required to convert the whole farm, see 5.5 in case whole
farm cannot be converted at one time. Areas converted to chemical-free production must not be
alternated (switched back and forth) between chemical-free and conventional production methods.
In cases where a whole farm is not converted at one time, it may be done progressively
whereby these standards are applied from the start of conversion on the relevant fields. Conversion
from conventional to chemical-free production should be effected using permitted techniques as
defined in these standards. In cases where a whole farm is not converted at the same time, the holding
must be split into 2 units. The responsible farmer should guarantee:
o
A clear boundary between the chemical-free and the conventional sectors to eliminate
contamination.
o
That the same varieties are not produced in both sectors: chemical-free and
conventional (parallel production), the varieties should be clearly distinguishable.
o
The conventional areas are not switched back and forth between chemical-free and
conventional management.
o
The whole farm will be included in a conversion plan that will formally bind the
producer to gradually incorporate plots or areas, completing the conversion of the last
plots within a three (3) year period.
24
For pest management and control the following measures, in order of preference, should be
used:
a) Preventative methods, such as disruption and elimination of habitat and access to facilities by pest
organisms, should be the primary methodology of pest management;
b) If preventative methods are inadequate, the first choice for pest control should be
mechanical/physical and biological methods;
Pests should be avoided by good manufacturing practice and proper hygiene. Pest control
measures within storage areas or transport containers may include physical barriers or other treatments
such as sound, ultra-sound, light, ultra-violet light, traps (pheromone traps and static bait traps)
controlled temperature, controlled atmosphere (carbon dioxide, oxygen, nitrogen), and diatomaceous
earth. Use of substances not listed in Annex or post harvest or quarantine purposes are not be
permitted on products prepared in accordance with these standards and would cause chemical free
produced foods to lose their chemical free status.
Packaging materials should preferably be chosen from bio-degradable, recycled or recyclable
sources.Product integrity should be maintained during any storage and transportation and handling by
use of the following precautions:
•
Chemical free produced food stuff must be protected at all times from co-mingling with nonchemical free products; and
•
Chemical free products must be protected at all times from contact with materials and
substances not permitted for use in chemical free farming and handling.
Where only part of the unit is certified, other products not covered by these standards should
be stored and handled separately and both types of products should be clearly identified. Bulk stores
for chemical free product should be separate from conventional product stores and clearly labelled to
that effect. Storage and transport containers for chemical free produced food must be clean using only
methods and materials permitted in organic and chemical free production.
Measures must be taken to prevent possible contamination from any pesticide and substance or
other treatment not listed before using a storage area or container that is not dedicated solely to
chemical free products.
25
26
27
28
29
30
31
Source: Cambodian Organic Agricultural Association (COrAA) (2013): Standards for Organic Crop
Production in Cambodia
32
33
Source: Perez, I, Gooc, CM, Cabili, JR, Rico M, Ebasan, MS, Zaragoza, M, Redondo,A, Orbita, RR,
Lacuna, M. (2015).
34
35
II.
ORGANIC AGRICULTURE CAN FEED THE WORLD
Several of the high profile advocates for conventional agricultural production have stated that
the world would starve if we all converted to organic agriculture. They have written articles for
science journals and other publications saying that organic agriculture is not sustainable and produces
yields that are significantly lower than conventional agriculture.
The push for genetically modified organisms (GMOs), growth hormones, animal feed
antibiotics, food irradiation and toxic synthetic chemicals is being justified, in part, by the rationale
that without these products the world will not be able to feed itself.
Europe, North America, Australia and Brazil are in the process of converting a large
percentage of their arable land from food production to bio fuels such as ethanol in an effort to
establish viable markets for their farmers. The latest push in GMO development is BioPharm where
plants such as corn, sugarcane and tobacco are modified to produce new compounds such as hormones,
vaccines, plastics, polymers and other non-food compounds. All of these developments will mean that
less food is grown on some of the world’s most productive farmland.
The reality is that the world produces more than enough food to feed everyone and has more
than enough suitable agricultural land to do it. Unfortunately due to inefficient, unfair distribution
systems and poor farming methods, millions of people do not get adequate nutrition.The mood of the
community has changed. They are now confident and very importantly they are empowered with the
knowledge that they can overcome the problems in their community (Diamond, J. 2005).
One of the most important aspects of the teaching farmers in these regions to increase yields
with sustainable/organic methods is that the food and fibre is produced close to where it is needed and
in many cases by the people who need it. It is not produced half way around the world, transported and
sold to them. Another important aspect is the low input costs. They do not need to buy expensive
imported fertilizers, herbicides and pesticides. The increase in yields also come with lower production
costs allowing a greater profit to these farmers. Thirdly the substitution of more labour intensive
activities such as cultural weeding, composting and inter cropping for expensive imported chemical
inputs, provides more employment for the local and regional communities. This employment allows
landless laborers to pay for their food and other needs.
The data shows that it is possible to get very good yields using organic systems. This is not
uniform at the moment with many organic growers not producing at the levels that are achievable.
Education on the best practices in organic agriculture is a cost effective and simple method of ensuring
high levels of economically, environmentally and socially sustainable production where it is needed.
Organic agriculture is a viable solution to preventing global hunger because:
36
1. It can achieve high yields;
2.
It can achieve these yields in the areas where it is needed most;
3.
It has low inputs;
4. It is cost effective and affordable;
5. It provides more employment so that the impoverished can purchase their needs;
6. It does not need any expensive technical investment.
INCREASED INTEREST IN NUTRIENT BALANCE STUDIES: THE NEED FOR
INCREASED AGRICULTURAL PRODUCTION
Direct or indirect assessment of nutrient budgets continued at the heart of expansion in
agricultural production. By far most nutrient balance studies include one or more of the so-called
macro nutrients: Nitrogen (N), Phosphorus (P) and Potassium (K).
N is essential for the production of plant proteins. It is very mobile, both in soluble and
gaseous forms. P is also essential for plant proteins, but is far less mobile and not susceptible to
leaching or gaseous losses. On the contrary, P is for the larger part present in chemical components
that are not directly accessible to plants. K is essential for formation, transformation and transport of
carbohydrates and also for protein synthesis. Crop residues often contain considerable quantities of K,
making recycling important.
Although less mobile than N, and not present in gaseous forms, part of the K in the soil is
mobile in solution and is therefore susceptible to leaching (Tisdale et al., 1993). Application of early P
fertilizers, based on basic slag, a by-product from the steel industry, enabled intensification and
expansion of agriculture. Subsequently, artificial N fertilizers were developed and broadly adopted. In
the late 20th century, intensification and expansion of food and fiber production, particularly in the
developing world, were driven by the use of nitrogen fertilizers (‘Green Revolution’), often associated
with mining of other nutrients, particularly K and P. In parallel , increasing understanding of the
biological processes underlying plant production led to identification of ever more essential plant
nutrients, allowing agricultural production on previously unused or under-utilized areas for which
micro nutrients, such as copper, zinc, and molybdenum, were recognized as the primary limitations.
The rapid increase in agricultural production associated with the green revolution in the last
four decades of the 20th century outpaced the increase in population, so that average per capita
consumption of food increased. These gains resulted from a combination of factors, i.e. an increase in
the area of land cultivated, development and adoption of higher yielding varieties of the major staple
crops, particularly wheat, rice, and maize, and increased use of irrigation, fertilizers, pesticides, and
herbicides, which enabled realization of the yield potential of these improved varieties.
37
Despite improvements, in Asia per capita production has increased but with production risks
in more marginal areas, including semi-arid, sloping and flood-prone lands or those characterized by
‘acid soils’, and with accessibility to food being highly unequal, resulting in food insecurity and
malnutrition for still a considerable percentage of people, in particular the poorest and most vulnerable
in South and Southeast Asia (Olk, D.C., Van Kessel, C., & Bronson, KF., 2000).
The recent increases in agricultural production have been associated, almost proportionally
with increases in the use of fertilizers. In fact, the differential increase in agricultural production in
different regions is related directly to the expansion in fertilizer use, which has been greatest in parts
of Asia, especially China, and least in sub-Saharan Africa. By far the greatest contribution to the
increase in fertilizer use is largely accounted for by N fertilizer, with much lower growth figures, and
even a recent decline in absolute terms for K and P fertilizers.
To meet the challenge of providing adequate food to all regions of the world, agricultural
production must increase substantially and land degradation must be reduced and eventually reversed.
This will require appreciable increases in resource utilization efficiency and the development of more
sustainable production systems. While many aspects of production systems need to be addressed, the
efficient use of nutrients is critical, which explains the recent high interest in nutrient balance analyses.
A major application for nutrient balance analyses is in management of fertilizers and other
nutrient input sources. At field and farm level, such analyses can be part of the process of developing
recommendations or decision support systems for inorganic and organic inputs. At higher levels, they
can be used in planning the geographic distribution of inputs, such as fertilizers, to match supply and
demand. At still higher levels, such information is valuable for developing strategies for the
production and/or import of fertilizers. In a slightly different way, nutrient balance analyses feed into
management tools at different scales. At field and farm level, they can be utilized to develop land use
plans, including annual and mufti-annual/perennial cropping patterns, management of cultivation,
irrigation, and fertilizer application, and as part of economic analyses. At higher levels, they are a
management tool for developing infrastructure (roads, storage, etc.), government policies and strategy
development for the private sector as often being interrelated by regulations or based on partnerships.
EXAMPLES OF NUTRIENT BALANCE ANALYSES
The conceptual nutrient balance model, used in the nutrient balance study of Stoorvogel, J.J. &
Smaling, E.M.A. (1990) includes five nutrient input components and five output components:
Inputs: Outputs:
1. Mineral fertilizers: Harvested product.
38
2. Manure and other organic inputs: Removed crop residues.
3. Deposition by rain and dust: Leaching.
4. N-fixation : Gaseous losses.
5. Sedimentation : Erosion.
Starting from this conceptual model, annual partial nutrient balances (also referred to as ‘farm
gate balances’) for N, P and K were calculated as: = Input – Output = (fertilizers + organic inputs from
outside the field/farm) – (removal from field/farm in products and crop residues)
These balances exclude inputs through (biological) nitrogen fixation, wet and dry deposition,
sedimentation, run-on, and nutrient uptake from exploration of sub-soil layers by deep roots and
outputs by leaching, erosion, run-off, and gaseous losses.
While it is acknowledged that partial budgets must be interpreted with caution, the relatively
accurate, rapid, and simple assessment of partial nutrient budgets can be of great value, especially if
consideration is given to the plausible magnitude of the full balance factors that are not included.
Traditionally, organic materials were recycled within the farm systems, although rates of application
must have been low.
Tree or shrub leaf litters from on-farm sources show promise for increasing soil organic matter
and improving soil fertility. Some studies have demonstrated very large and rapid responses to large
applications of legume leaf litter, however, in many cases the levels applied are impractical. Much
research has focused on nutrient management in the course of the growth cycle of the rice crop. It is
equally important to direct attention to generating management strategies that focus on a systems
approach to integrated nutrient management to sustain productivity and protect the resource base. The
introduction of leguminous species into rice mono-cropping systems can significantly enhance soil
fertility, as a result of the net input of biologically fixed N into the system, thus reducing the need for
external inputs. In the long run, the introduction of legumes can improve the nutrition of rice with
respect to other nutrients, particularly P, as the improved nitrogen fertility resulting from the legume
can increase the vigour of the rice plants, resulting in more extensive root growth, and thus improved
nutrient acquisition and nutrient use efficiency. Moreover, the successful introduction of legumes
requires addressing other nutrient problems, particularly P-deficiency. This can be of indirect benefit
to rice productivity through the improved P status of the soil.
On-station and on-farm trials on the use of pre-rice green manures have shown promising
results (in that it resulted in substantial increases in rice yields. However, adoption of the technology
by farmers presents problems, i.e. shortage of labour for green manure incorporation, chemical
fertilizer requirements of the green manure crop and shortage of seed. Legume crops, such as
39
mungbean and cowpea, have been extensively investigated, both as pre- or post-rice crops. This
technology is unlikely to produce the large increases in rice yield in the short term observed from
green manures).
However, the problems of adoption are smaller. Nevertheless, this technology is risky in
rainfed lowland conditions where inundation in pre-rice crops and water shortage in post-rice crops
may pose significant problems (Supapoj et al., 1998). Some problems that arise in these contexts are:
First, many research programmes do not include a dissemination and implementation phase,
i.e. promotion, scaling up and implementation of relevant research findings, or this phase is poorly
planned, funded and/or executed. Unfortunately, in many research programmes production of reports
and/or publications in scientific journals is considered more important than the impact on end-users.
Optimal dissemination and implementation of results generally receives less attention, because this
process does not match the skills and interests of the planners and implementers, or because career
possibilities within institutions are based on easily measurable factors, such as numbers of reports and
publications, not on the impact on farmers, which is much harder to measure.
Second, lack of consensus on guidelines results in minimal standardization in data collection,
management, interpretation, storage and dissemination. The resulting limited accessibility of reliable
data leads to repetition of research, which is inefficient. In general, this problem results from lack of
research collaboration and co-ordination at all scales, and within as well as between institutions and
countries. This is associated with the problem of overlapping mandates and responsibilities among
different groups involved in the research, development and extension chain, which is common for
R&D in many parts of the world. These problems occur both intra- and inter-institutionally,
particularly between the research units and the extension services and end-users.
Many of these problems are difficult to address directly, as they are rooted in inadequate staff
and funding, as well as in competition for human and financial resources and ideas. There is lack of
donor coordination and long-term donor commitments to structural development needs. Above all,
there is a lack of demand-driven, development- and client-oriented collaborative and genuinely
participatory R&D efforts based on clear multi-level partnerships among community members,
communities, government agencies, NGOs involved in participatory research and piloting, regional,
national and international research institutions, the private sector and last but not least donor
organizations.
CROP ROTATIONS
There is a need to evaluate species, particularly legumes, for their suitability as components of
the farming systems of the region, either as pre- and/or post-rice crops or elsewhere in integrated
40
farming systems without serving as rotation crops for rice as such. Such evaluations should pay
attention to management requirements for establishment, nutrient supply, harvesting practices, and
water use within the whole system. In addition, other aspects should be considered, such as the quality
of the residues as a criterion for the value of a species as a soil amendment, for increasing nutrient
supply and soil organic matter (SOM) content. Within this context, crop residues production may take
precedence over economic yield (Schiere et al., 2004).
BIOPHYSICAL CONSTRAINTS AND CHALLENGES IN AGRICULTURE
There are limitations and challenges that must be observed in every farm, as following:
Constraints
I.
Dominance of inherently marginal soils - Coarse textures, limited nutrient pools, low
effective cation exchange capacity (ECEC), low base saturation (BS), low soil organic
matter content (SOM), etc...
II.
Erratic rainfall and lack of irrigation water
III.
Micro-topographic variability
I, II and III result in high spatio-temporal variability along micro-topographic catenae.
Possible solutions
I.
Design and adoption of innovative dynamic and site-specific water and nutrient
management strategies/land-use systems; Combinations of organic and inorganic inputs
and cropping system approaches; inputs synchronized with crop requirements and weather
conditions; slow-release fertilizers; leaching and erosion control; improved G×E
interaction; site-specific (topographic position) land use systems and nutrient management.
II.
Integrated farming, focus on farm (and off-farm) activities not merely relying on the
quality of natural resources alone, but very much on farming system innovations (e.g.
zero-grazing, fish farming, etc.)
III.
Small-scale irrigation (ponds, pumps); larger irrigation systems and biophysical
improvements (e.g. land levelling), but only if and where biophysically and socioeconomically appropriate and feasible.
41
Socio-economic constraints and challenges
Constraints
I.
Generally low education level (partly because of brain drain to urban centres);
II.
Limited capacity of private sector; lack of capital;
III.
Limited economic diversification; vulnerability;
IV.
Relatively weakly developed markets and unstable (world) market prices;
V.
Insecure land rights and lack of quality land (partly a biophysical constraint) for resourcepoor farmers;
VI.
Increasing urban population and increasing demand for agricultural products (partly
related to economic crisis and international market situation).
Possible solutions
I.
Main focus on quality education, equity and empowerment of rural poor, gender equity;
II.
Create enabling conditions and opportunities in rural areas;
III.
On- and off-farm (livelihood) diversification (agriculture not only focus);
IV.
Start-up initiatives, partnership building, creation of interest groups (institutional
development at community level);
V.
Improved land use policy based on multi-stakeholder involvement and insights;
VI.
Emphasis on environmental protection; reduced pressure on marginal lands;
VII.
Reduced dependence on, or influence of fluctuations in international markets;
VIII.
Inherent (including institutional and policy-related) R&D constraints and challenges.
Technologies and qualifications
Constraints
I.
Sometimes technically inappropriate; Inappropriate in broader (holistic) context:
biophysical, socio-economic, cultural and/or political constraints may be overlooked;
II.
Too static (focused on current state, instead of taking into account possible development
trends; subject may become outdated before results appear);
III.
Too much site-specific/too little orientation on site-specificity; how to scale-up or account
for site-specificity/diversity?;
IV.
Disregard for or lack of time to realize ultimate objectives/implementation/impact (often
due to deviating agendas);
V.
Lack of capacity (time, human, financial, organizational, and institutional);
42
VI.
Lack of coordination and priority setting (lost time and double, isolated or irrelevant
efforts partly due to competition for financial and human resources and ideas);
VII.
Inappropriate extension.
Possible solutions
I.
Participatory and interdisciplinary approaches
a. Identification of constraints for proper implementation
b. Strengthen institutional settings for the use of participatory approaches;
II.
More sharing, collaboration and partnerships both vertically and horizontally.
c. Strengthen partnerships between research and extension systems on one hand, and
farmers and their organizations on the other hand.
d. Strengthen partnerships among national and international R&D institutions, among
different farmer and community-based;
II.
Organizations and among donor organizations and between these different stakeholder
groups;
III.
Improved research planning, including priority setting
a. Consistent focus on objectives, final goals, sustainability (exit strategies) and impact
b. Reduction or elimination of non-constructive deviating (personal / secondary) agendas;
III.
Quality education;
IV.
Changes in attitudes.
GROWING LOWLAND RICE
These constraints include ineffective farmer organizations and groups, low yield and poor
milling quality of local rice varieties, poor marketing arrangements, inconsistent agricultural input and
rice trade policies, poor extension systems and environmental constraints. These environmental
constraints include poor drainage and iron toxicity in undeveloped lowland swamps, poor management
practices (Roder, W., Keoboulapha, B., Phengchanh, S., Prot, J.C., & Matias, D., 1998)
The unavailability of lowland rice production manuals has also been Farmers need to be taught
how to prepare land and nursery beds, quantity of seed to plant per hectare, when to transplant their
rice, how to apply inputs such as chemical fertilizers and herbicides, the weeding regimes and disease
control methods, among others.
Major lowland production constraints
43
Biotic
•
Weeds;
•
Insects;
•
Diseases - Rice yellow mottle virus (RYMV) – Blast - Sheath rot – Smut.
•
Iron toxicity;
•
Salinity/alkalinity problems in the irrigated lowland production system.
Abiotic
Choice of land
•
Choose fertile land with good water retention capacity (contain some clay
and/or organic matter, i.e. loamy soil); clayed soils are most desirable;
•
Heavy soils of valleys and fadamas are preferred;
•
Consult Soil Survey and Testing Service of the Institute of Agricultural
Research and Training (IAR&T), and any other reputable soil-testing unit if
growing rice for one or more consecutive years on the same piece of land.
Recommended lowland varieties
•
Early maturing (<90–100 days): FARO 44 (SIPI) and ‘etumbe’ (local).
•
Mediummaturing (100–120 days): FARO21, 26, 29, 52 (WITA 4), 57 TOX
4004-43-1-2-1, and others.
•
SUAKOKO 8 and FARO15: Suitable for iron toxic areas.
•
Late maturing (>120 days): FARO 10, 12, 13, 16, 17, 19, 24, 28, and others.
•
Gall midge-affected areas: Cisadane (FARO 51).
Choice of seed
•
Use good quality seeds with no insect damage and no contaminants (weed
seeds, stones, other seed types) with high percentage of viability (>80%).
•
Seed company.
•
Other rice farmers.
Seed dormancy
44
•
Dormancy is the failure of good quality mature seeds to germinate under
favorable conditions. Dormancy of freshly harvested seed should be broken
by using heat treatment at 50°C in an oven if available or by placing the
seeds on a plastic sheet and covering with itself or another under direct
sunlight for 1 or 2 days. Acid treatment may also be used.
•
Acid treatment: soak seeds for 16 to 24 hours in 6 ml of concentrated nitric
acid (69% HNO3) per liter of water for every 1 kg of newly-harvested seeds.
After soaking, drain acid solution off and sun-dry the seeds for 3 to 5 days
to a moisture content of 14%. Store in dry conditions for sowing.
•
Conduct germination test on seeds to establish rates to use based on seed
viability. Avoid seeds of mixed varieties. Seed viability testing and seed
requirement
•
When the seed viability is not known, carry out a simple seed viability test
to guide the actual seeds required for sowing. in a dish with lid (use Petridish if available) and put in 100 temperature for 4–5 days to allow
germination.
•
Then count the number of sprouting seeds (only those with shoots >1 cm).
If 75 germinating seeds are counted, it means the viability rate is 75%
(%germination).
•
If the seed rate is 80 kg/ha, the actual quantity of seeds to be used for
sowing is calculated.
Fertilizer application
Fertilizer should be applied based on the residual nutrients found after soil
testing, and the expected yield and the type of fertilizer materials available.
The farmer should strive to obtain fertilizer recommendations based on the
analyses of soil samples.
In situations where it is not possible to conduct a soil test due to high cost and
unavailability of analytical services, or when the farmer is running out of time
because the crop is subnormal in growth, the general recommendations in this
handbook should serve as a guide.
General fertilizer recommendation based on agroecology for humid forest:
Apply 60 kg N, 30–60 kg P2O5 and 30 kg of K2O per hectare.
Mixing fertilizers
45
•
When it is required to apply two or more elements and the desired
compound fertilizer is not available but the straight fertilizers are available
it may weigh and mix the fertilizers before application. This is particularly
important for large mechanized rice farms.
•
However, note that not all fertilizers are compatible when mixed. For
example, if basal N is necessary and you need to apply N and P as basal, do
Minot ammonium sulphate with rock phosphate, or urea with superphosphate. The elements will react with one another and become less
effective.
Fertilizer calculations
•
Recommended rate: 100 kg N – 60 kg P205 – 60 kg K20 per hectare (irrigated system).
•
Compound fertilizer available: NPK 15–15–15.
To calculate the amount of NPK 15–15–15 + urea to get the recommended rate.
•
In the recommended rate, there is less P and K than N.
•
Formula: Quantity required R = Recommended rate; i.e. 60 kg P205/ha C =
Fertilizer grade; i.e. 15 for P205.
•
Amount of fertilizer = Q = 60/15 kg × 100 = 400 kg
•
Since for K20, also R = 60 kg K20; C = 15, it means that the amount of
fertilizer = 400 kg
•
Therefore, if you take 400 kg of 15–15–15, you will get 60 kg P205 and 60
kg K20.
But how much N will you get?
•
The amount of N in 400 kg ( = Rate ) of 15–15–15 NPK is: R = (Q × C)/100 - 400 kg × 15
(100)
•
If 100 kg N is required and NPK supplies 60 kg N, the balance of 40 kg N will be supplied
fromurea.
Amount of urea:
46
•
46kg N x 100 kg urea (46 kg N is contained in 100 kg urea)
•
Therefore, 40 kg N= 40 × 100 = 87 kg.
•
Apply 400 kg NPK 15–15–15 as basal before transplanting and 87 kg (1¾bags) urea as
topdressing in 2 equal splits (mid-tillering and at about panicle initiation).
Pesticide safety: Pesticides can be highly poisonous and it is therefore important to take
adequate safety precautions when transporting, storing or handling agricultural and other pesticides.
Misuse of pesticides and other chemicals used in agriculture is responsible for many serious injuries
and deaths in rural areas each year.
Always readand follow thoroughly the instructions printed on the pesticide label. Do not
remove the label from the containers or boxes. Make sure that the chemical you want to use is still
permitted for use in your country. Do not mix agrochemical unless you have clear label guidance that
the chemicals are compatible.
Always wear suitable protective clothing. Rubber gloves, overalls, a face mask and respirator
are recommended when mixing pesticides. Gloves, long trousers and a long-sleeved shirt should be
worn when applying less hazardous pesticides. This clothing can be uncomfortable to wear in humid
climates but it is important that pesticides are not allowed to enter the body through the skin, mouth or
lungs. Keep and wash this clothing separately from other garments.
Handle pesticides with care. Inspect pesticide containers for leaks before handling them.
Avoid splashing or spilling liquids and causing powders to puff up or be spilled. Avoid inhaling dusts
or vapors. Never work alone when handling the more toxic pesticides. Do not re-enter the treated area.
In case of injury or accidental swallowing etc., go immediately to the nearest antidote: Make sure you
know the antidote of the chemical you are using so that it can be used in case of accidental intoxication.
Never eat, smoke or drink when handling pesticides. Always wash thoroughly with soap and
water after handling agrochemical. If possible to have a container of water readily to hand for
emergency wash use. Only use pesticides when the weather is still and dry. Read the label for
appropriate instructions. Do not use agrochemical designed for a particular crop, e.g. cotton, on
another unrelated crop such as cabbage or onion. Nor should crop pesticides be used to treat animals.
Keep an accurate record of pesticide usage, including quantity used, rate and date of application.
STORAGE OF PESTICIDES
Store pesticides in a building or storage area reserved solely for this purpose and which can be
securely locked. Keep pesticides in a store supplies. Prevent unauthorized people, especially children,
47
from having access to or contact with pesticides. Store pesticides in the original labeled container and
protect the labels in storage so that they remain readable.
Store large quantities of herbicides in a separate building or area from other pesticides.
Management of leftover agrochemical: Always try to prepare only the quantity that is needed for the
area to be treated so as to avoid having remaining chemicals, no matter how much or how little they
are, should never be thrown away behind the store or in a nearby stream or bush.
They should not be transferred to improper containers such as an empty food, feed, medicine
or beverage container nor misplaced, but must be securely kept in the store in the original container or
box until they can be used or disposed of safely. Small quantities of chemicals can be added to your
next spray tank in the correct quantities.Washings from used chemical containers can also be added to
the spray tank.
Transportation: Transport pesticides in an upright position in the open box of a truck, securing
all containers. Do not transport pesticides in the passenger area of any vehicle.D Do not allow anyone
to ride in the back with the pesticides.
Disposal of pesticide containers: Rinse all pesticide containers three times prior to disposal to
reduce environmental contamination. Do not throw empty pesticide containers carelessly about the
farm or into rivers.Where there is no designated pesticide containers disposal site, such containers
should be buried deeply in a properly labeled area that is far from water sources (Noyes R.T. et
al.,1991).
CAPACITY TO ADOPT ORGANIC CERTIFICATION
Generally, the principles point to the sustenance and enhancement of the ecosystems and
organisms including human beings. Input reduction is also emphasized complemented by reuse,
recycling and efficient management of materials and energy in order to maintain and improve
environmental quality, conserve resources and produce high quality, nutritious food that contributes to
preventive health care and well being (IFOAM, 2006).
RECOMMENDATIONS ON GOOD AGRICUTURAL PRACTICES FOR RICE
WATER SOURCES
• Water applied to rice cultivation should not be obtained from sources where the environment
is risk to contamination with any harmful substance and its quality is suitable for cultivation. It
shall not be waste water from industrial activities or others that may cause hazardous
48
contamination. If necessary to use, it shall be clarified that the water has been treated to
improve the quality suitable for rice production.
•
If it is doubted that water may be contaminated with hazardous substances, it should be
collected at random at least once before rice cultivation. The sample should be submitted to an
official laboratory or an officially accredited laboratory for any contamination. The sampling
practice and the results must be kept as the evidence.
•
Water resources and farm environment should be conserved for rice cultivation.
PLANTATION AREA
• The production plots must be noted in the records. The details consist of farmer’s name,
contact address, plot keeper (if any) with contact address, farm layout, crop type and variety
name, history of the farm land utilization at least in the past three years, and other details.
•
If any risk to hazardous substance contamination, the soil should be collected at random and
analyzed at least once before rice cultivation by an official laboratory or officially accredited
laboratory. The results must be kept as the evidence.
APPLICATION OF PESTICIDES
• Application of hazardous substances shall be complied with the relevant laws. The label shall
indicate the registration number and the application instruction to rice cultivation. Application
of the substances shall be ceased before harvesting and complied with the duration indicated
in the label or the official recommendations.
•
Rice for export, the hazardous substance applied shall not be those indicated in the prohibited
list of the trading countries.
•
Application of hazardous substances shall follow the instruction on the official label
authorized. Application of pesticides must comply with the identified pests found in the rice
field and the official recommendations of the Rice Department or Department of Agriculture.
•
The farmer and labors who work in the plant pest protection sector should understand the
nature of pests, select the appropriate pesticides and application rate, and select suitable
sprayers and nozzles with the correct application. It is recommended that, the equipment
should be in good condition and be ready all the time by consistent checking. To prevent
contamination from pesticides, the applicants must put on protective clothing covering the
body and some protective accessories, such as face masks or nasal masks, rubber gloves, hats
or caps and rubber boots.
•
All the prepared solution should be completed at one application. Do not leave any excess
solution in the tank of the equipment.
49
•
Hazardous substance must be prepared at the recommended concentration. The substance
should be diluted by adding water to the specified volume and stirred to get a homogeneous
dilution.
•
Application of hazardous substance should be done in morning or evening at still wind. Avoid
to apply the substance under strong sunny or windy. The applicants must be at windward
position during working.
•
After spraying hazardous substance, the applicant must bathe and shampoo, change clothing at
once. The used clothing must be cleanly washed.
•
When the pesticide is applied completely, the equipment must be well rinsed two to three
times with water.
•
If the hazardous substance is not depleted at one application, the remaining chemical in the
container shall be tightly closed and kept in the agricultural hazardous substance storage.
•
The empty container of hazardous substance must be to prevent reusing. destroyed to prevent
reusing. The damaged containers should be collected at a particular place for elimination later
or buried under ground. It must be ensured that, the hazardous substance should not cause any
contamination to water resource and the dept is enough to prevent unearthing from animals. It
is prohibited to burn the hazardous substance container.
Agricultural hazardous substance storage
•
Containers of agricultural hazardous substances used in production practice must be kept in a
particular room with properly closed for safety and prevent the exposure to sunlight and
rainfall with good ventilation. The store room should be well assigned and partitioned to
prevent any contamination to food and environment. There should be a set of first aid for an
emergency need, such as, eye cleaner, clean water, sand and fire extinguisher.
•
Each hazardous substance must be kept in a sealed container with clear label and stored in
categorized group. They should be kept separately from fertilizers, plant growth regulator, and
other plant supplements. Once a container of hazardous substance is opened, the remaining
chemical shall be kept in its own container, do not transfer to another one.
•
Hazardous substance that is prohibited to be produced, imported, exported, or in possession
according should not be kept in the storage or in cultivating field.
QUALITY MANAGEMENT IN PRE-HARVEST PRODUCTION
The Production for the right variety of paddy. The following practice is recommended for
controlling off type rice in paddy after being harvested and threshed. This admixture is allowed not
50
exceeded 5 % in the standard. This amount includes red rice. Use qualified rice seed from an official
agency or other seed source certified by the Rice Department or competent authorities.
Qualified seed should contain at least 98% purity, not less than 80% germination, admixture of
other rice variety shall not exceed 0.5%. It can be obtained or purchased from the following sources:
(1) The official agencies such as Rice Seed Centers, Rice Research Centers under the Rice
Department; or
(2) Agricultural Cooperatives, Agricultural Promotion and Rice Seed Production Community
and other competent authorities certified by the Rice Department or other assigned agencies; or
(3) Farmer produces his own seed. The seed shall be produced from an isolated area from
paddy commodity production field, or the seeds produced from the selected area in paddy field that
showed a uniform plant performance and any off type plants have been eliminated during growing.
•
Seed preparing for wet seeded practice or transplanting seedling should be put in a gunnysack,
a cotton bag or a bag made from any material providing good water drainage. The bag is
steeped in water for 12 to 24 hours then take it out from water to drain and cover the wetted
bag with thick sailcloth to incubate the seeds for 36 to 48 hours. Sprinkle the bag occasionally.
After incubation period, a small shoot and a small root will grow from the germinated seed.
The seeds are ready for wet seeded or seedling preparation. For dry seeded practice rough rice
seed can be applied directly on rice field.
•
Planting and Cultivation. The practice is applied to control off type rice plants not exceeding
to 3%, in this amount including red rice not more than 1%. This level of adulteration can be
anticipated the admixture of other rice variety not exceeding to 5% with 2% red rice in the
commodity.
Planting season
•
Rice should be planted at an appropriate time depending on the variety. It is suggested to
avoid unfavorable weather during plant development, for example, too warm or too cold
weather during blooming stage, and heavy rain at harvesting.
•
Appropriate time for rice planting in main crop and off season crop in irrigated area are as
follow;
•
Improve soil fertility.
51
Improving soil fertility should be done according to the following;
• Rice stubbles and straws should not be burnt after harvest. It is suggested to left them decompose
naturally or plough and turn over them in to muddy soil or apply a bio extract during land preparation
for wet seeded practice to accelerate decomposition of the bio-mass.
• To improve low fertile soil, application organic fertilizer is suggested, such as compost, manure, rice
husk, humus, green manure etc. Spread 500 to 1000 kilogram of organic fertilizer per rai throughout
the field and plough over. Leave it to decompose for two to three weeks to complete gasification
process that will be harmful and toxic to rice plant.
• Two months before rice cultivation, seeds of legume may be applied as green manure such as
Sesbania rostrata, Mung bean, cowpea, or Crotalaria juncea. These seeds should be sow at the rate of
five kilograms per rai or Jackbean seed 10 kilograms per rai. When the plants grow for 50 days or
blooming, they are ploughed.
Seed rate for transplanting, wet seeded and dry seeded practices should be as following:
• 5 to 7 kilograms per rai for transplanting.
• 10 to 20 kilograms per rai for wet seeded.
• 10 to 20 kilograms per rai for dry seeded.
Seed rate for wet seeded and dry seeded practices may be adjusted depending on soil condition
and pests infection. If the soil surface is plane without any interference from rats, birds and weed, seed
rate can be reduced to 10 kilograms per rai. If the soil surface is uneven or bumpy and contains serious
pest infection, therefore it is necessary to increase seed rate.
Soil Preparation and Planting Method
Transplanting practice should be done as follow;
(1) Seedling nursery
52
•
The seedbed should be prepared by starting from first plowing in lengthwise of the field. The
second plowing in crosswise should be done 7-10 days after. Water should be applied into the
field subsequently after plowing to flood the muddy soil, then harrowing and paddling
processes.
•
The prepared land should be partitioned into small seedbeds, 1-2 m. wide with the length
along the field. A small furrow of 30 cm. wide is set between seedbeds for water drainage.
•
Rice seeds are sown uniformly on the seedbeds at the rate of 50-70 gm. per sq. m.
•
The seedbeds re maintained at saturated moisture for seed germination by draining out the
flooding water. After the emergence of seedling, gradually increase the water level of the
seedbeds according to the height of the seedling, but not exceeds 5 cm. from the soil surface.
(2) Transplanting
•
Planting field should be started from first plowing in lengthwise of the field. The second
plowing in crosswise should be done 7-10 days after. Water should be applied into the field
subsequently after plowing to flood the muddy soil, then harrowing and paddling processes.
The water level should be maintained at approximately 5 cm. From the soil surface.
•
Transplanting is made by using approximately 25 day-old seedlings.
•
Spacing between rows is recommended at 20 cm and between hills at 20 cm with the number
of 3 to 5 seedlings/hill.
•
Water level in the field should be maintained at 5-10 cm. that appropriate to the plants growth.
•
Water should be maintained all the plant growth duration, especially the period of panicle
initiation to blooming
•
15 to 20 days after 80% of plants bloomed; remaining water should be drained depending on
soil type.
Wet seeded Practice should be done as follow;
•
Planting field should be started from first plowing in lengthwise of the field. The second
plowing in crosswise should be done 7-10 days after. Water should be applied into the field
subsequently after plowing to flood the muddy soil, then harrowing and puddling processes,
then leveling the muddy surface.
•
Prepared field should be partitioned into small plots of 5-10 m. wide with the length along the
field. A small furrow of 30 cm. wide should be set between the plots for water drainage.
•
Rice seeds should be sown or broadcasted uniformly on the plots at the rate of 10 to 20 kg./rai.
53
•
Drain off flooding water after sowing and keep the soil saturated with moisture for seed
germination, then gradually increase the water level according to the height of the plants, but
not exceed 10 cm. from the soil surface.
•
Water should be maintained all the plant growth duration, especially the period of panicle
initiation to blooming
•
15 to 20 days after 80% of plants bloomed; remaining water should be drained depending on
soil type.
Dry seeded practice should be done as follow;
•
Planting field should be started from first plowing in lengthwise of the field. The second
plowing in crosswise should be done 15-30 days after with hand weeding at the same time.
•
Rice seeds should be sown or broadcasted uniformly on the plots at the rate of 10 to 20 kg./rai.
•
Soil should be plowed to incorporate rice seed under it. The moisture will accelerate seed
germination. If the seeds incorporated too deep under the soil, at heavy rain, the seed would
not evenly germinate and rot.
•
After sowing, keep the field from being flooded but containing moisture sufficient for seed
germination. Slowly increase water level according to plant height. Be careful that the plants
are not submerged under water and not exceed to 10 cm. from soil surface.
•
Be sure that rice plants have sufficient water to grow, especially at the stage of panicle
initiation and blooming.
•
15 to 20 days after 80% of plants bloomed; remaining water should be drained depending on
soil type.
Fertilizer application
Fertilizer application should comply with good cultural practice for rice as follow;
•
Plot size should be known for accurate fertilizer application
•
Dike around rice plot must not have any water leakage before fertilizer application.
After applying fertilizer for three to five days, water can be flow normally:
•
Before fertilizer application, water level should be maintained at 5cm.
•
Eliminate any weed in rice before fertilizer application, especially when rice plants develop at
early stage.
•
Apply fertilizer, its rate and time of application appropriate to rice variety and soil type.
54
•
Calculate amount of fertilize use correctly or apply fertilizer sufficient for the plant
requirement.
•
Clay soil: the recommended basal application is 20-25 kg./rai of either of the following
compound fertilizers, 16-20-0 or 18-22-0 or 20-20-0. Top dressing application is 5-10 kg./rai
of urea or 10-20 kg./rai of ammonium sulfate or ammonium chloride.
•
Loam, sand and sandy loam soils: the recommended basal application is 20-25 kg./rai of either
of the following compound fertilizers, 16-16-8 or 18-12-6. Top dressing application is 5-10
kg./rai of urea or 10-20 kg./rai of ammonium sulfate or ammonium chloride.
The use of organic fertilizer in rice cultivation must be decomposed completely. Method of
producing and applying should not introduce any contamination that is harmful to consumers.
The use of chemical fertilizers incorporated with organic fertilizers in rice cultivation, the
organic fertilizer enhances an improvement in physical and biological properties of soil. It increase
micro organism and contains more supplemental elements than chemical fertilizer. It also absorbs
nutrients and slow down leaching of chemical fertilizer. Application of chemical incorporated with
organic fertilizers depends on soil type as follow;
•
Clay soil: organic fertilizers such as manure, composts of rice straw, rice husk, or husk ash, at
the rate of 500 to 1,000 kg./rai., as well as Azola at the rate of 50 to 100 kg./rai are
recommended to apply to the rice field before planting. Green manure, such as legumes should
be planted at the seed rates of 5-10 kg./rai are also recommended. The green manure plants
should be plowed to incorporate them with soil before planting rice. The chemical fertilizer is
recommended for basal application at the rate 20-25 kg./rai of 16-20-0 or 18-22-0 or 20-20-0
formulated fertilizers.
•
Loam, sand, and sandy loam soils: before planting rice, organic fertilizers such as manure,
composts of rice straw, rice husk, or husk ash, are recommended at the rate of 500 to 1,000
kg./rai. Azola is also advised to apply at the rate of 50 to 100 kg./rai. Green manure, such as
Sesbania spp. or kenaf (Hibisens cannabinus) planted at the seed rates of 5 to 10 kg./rai are
also recommended. The green manure plants should be plowed to incorporate them with soil
before planting rice. The chemical fertilizer is recommended for basal application at the rate
20-25 kg./rai of 16-16-8 or 18-12-6 formulated fertilizers.
Consideration for fertilizer application
•
Use only one formula of fertilizer in each application.
55
•
The first figure of the above recommended compound fertilizer indicates the general rate
while the later figure is the rate to get a higher yield.
•
For basal application, the recommended rate of fertilizer may be split into twice, on the
planting date and rice tillering stage.
•
Top dress fertilizer means the fertilizer applies at panicle initiation stage of rice plant
•
Application of organic fertilizer every year induces the accumulation in the soil and reduce the
requirement of chemical fertilizer in the following year. So heavy application of organic
fertilizer accelerate the reduction of chemical use.
56
CROP ROTATION ON VEGETABLE FARMS
Crop rotation is one of the most effective tools for managing pests and maintaining soil
fertility, but there aren’t many specific recommendations for how to go about it. A common approach
on vegetable farms is to rotate crops by families. Another strategy is to alternate vegetable crops with
field or forage crops, such as small grains, alfalfa or clovers. Some growers try to rotate fields so they
are in cash crops one year and cover crops the next year. On farms with limited land for rotation out of
cash crops, sweet corn is a good crop to rotate with since it hosts very few insects or diseases that
affect other vegetables.
Too many growers rotate their crops using the ‘seat of their pants’ technique, relying on
memory and making decisions day by day when planting. To make the most of crop rotation you need
detailed records of where crops were grown in the past as well as a written plan for how crops will be
arranged in the future.
It is advisable to start by making a map of your farm and other fields you may use such as
rented fields. Label the fields or sub-fields with names and acreage. Make photocopies of the map and
at the end of each season fill one in and date it, noting any serious pest or soil problems in a field.
Prior to the growing season, fill in a new map with your best guess as to where crops will go,
depending on growing conditions, etc. Try to develop a plan that results in the most years possible
between planting similar crops in a given location.
As you plan, remember that rotation helps prevent some pests but not others. For insects that
over-winter near the crop they infested, such as Colorado potato beetle, European corn borer, or flea
beetle, it helps to plant host crops as far away as possible the next year. Having a barrier such as a road
or river between last year’s crop and this year’s can enhance the rotation effect. Rotation will not help
prevent insect damage from pests that migrate into the area, such as potato leafhopper or corn earworm.
For diseases that are soil-borne or over-winter in crop residues, rotating out of susceptible
crops is a key to preventing infection, as in the case of Phytophthora blight, early blight, and many
other diseases. However, host crops must be rotated far enough away to avoid infection through
blowing or washing soil.
Equipment that moves soil from field to field can also reduce the benefit of rotation. For some
diseases, such as clubroot of crucifers, susceptible weed hosts must be controlled if rotation is to be
effective. As with insects, rotation cannot prevent airborne diseases that move in from other areas,
such as downy mildew, nor can it prevent seed-borne diseases.
In addition to minimizing some pest pressure, rotating crops is also good for soil health
because it leads to changes in tillage, rooting depth and nutrient removal. Rotation is also a way to
57
maintain soil organic matter if plans include soil-improving cover crops, a practice that is critical to
sustaining productivity over time.
Always include winter cover crops in your rotation plans to minimize erosion and add some
organic matter back to the soil. Whenever possible, also use summer cover crops for warm-season
biomass production and weed suppression. In addition, to the extent possible, one should include one
or two year-long green manure crops to ‘rest’ fields from tillage for substantial periods of time while
allowing extensive cover crop root growth to occur. Thus, inter cropping cover crops and cash crops
can help maintain soil fertility and enhance biodiversity. However, this does not negate the need to
rotate cash crops among fields (Porciuncula F., L Galang, 2014).
CONSERVATION AGRICULTURE
Definitions
•
Conservation Tillage (CT): Any tillage and planting system that covers 30 percent or more of
the soil surface with crop residue, after planting, to reduce soil erosion by water. Where wind
erosion is the primary concern, any system that maintains at least 1,000 lb/acre (1.1 Mg/ha) of
flat, small grain residue equivalent on the surface throughout the critical wind erosion period.
The following define three broad classes of conservation tillage.
•
No-till or Strip-till (NT): A tillage/planting system where the soil is left undisturbed from
harvest to planting except for nutrient injection. Planting is accomplished in a narrow seedbed
or slot created by coulters, row cleaners, row chisels or roto tillers. Weed control is
accomplished primarily with herbicides. Less than 25% row width disturbance is considered
no-till.
•
Ridge-till (RT): A tillage/planting system where the soil is left undisturbed from harvest to
planting except for nutrient injection. Planting is completed in a seedbed prepared on ridges
with sweeps, disk openers, coulters, or row cleaners. Residue is left on the surface between
ridges. Weed control is accomplished with herbicides and when ridges are rebuilt during
cultivation.
•
Mulch-till (MT): The soil surface is disturbed prior to planting. Tillage tools such as chisels,
field cultivators, disks, sweeps or blades are used. Weed control is generally accomplished
with herbicides and/or cultivation.
•
Reduced Till (RDT): Any tillage system that leaves 15–30 percent residue cover after planting,
or less than 500 lb/acre (0.55 Mg/ha) of small grain residue equivalent throughout the critical
wind erosion period.
58
•
Conventional Till (CVT): Any tillage system that leaves less than 15 percent residue cover
after planting or less than 500 lbs/acre (<55 Mg/ha) small grain residue during the critical
wind erosion period. Generally involves plowing or intensive tillage.
Crop Management Factors
Weed Control: Conservation tillage systems most often result in increased reliance on
chemical weed control.
Weed control can be a significant problem in CT systems where pH
stratification affects herbicide activity or where residue cover may intercept herbicides rendering them
inactive. At times, emergency tillage is required to offset herbicide failures resulting in less than 30%
residue cover. In specific situations, the most effective herbicide compounds will require soil mixing
limiting the choice of CT systems. Conversely, CT systems can also afford reduction in herbicide use
when banded in strip- or ridge-tillage operations. Cooler soils in residue-laden zones may suppress the
emergence and competitive ability of weeds relative to the crop. Weed control in continuous cropping
systems are usually the most problematic for CT systems because weeds with similar biological
characteristics and growth periods to the crop tend to predominate over time. In these situations,
rotation of crop species may be the most effective weed control measure under CT. The introduction
of herbicide resistant crops has revolutionized CT weed control strategies in the maize belt but the
safety and ecological impact of these crops is being questioned.
Crop Rotation
Crop rotations allow selection of different herbicides, planting dates and tillage systems
resulting in greater opportunities to control weeds, disease and insect pests. Certain CT systems are
not amenable to crop rotations. For example, RT systems that require ridge construction during a row
crop season are unsuited to rotation with solid seeded or sod crops. This fact tends to limit the acreage
devoted to RT. Often CT systems alternate with crop rotations in response to residue management
needs or fertilization strategies. Crop rotations of all sorts are becoming the dominant cropping
strategy as they provide market diversity as well as management flexibility.
Soil Fertility
Stratification of soil chemical properties and nutrient distribution is a commonly observed
phenomenon of CT systems. Non-mobile nutrients such as P and K can accumulate in the upper
portions of the soil profile from surface placement of fertilizer materials and/or deposition from
59
decomposed residues. The extent of soil acidification produced by nitrification of ammonium N will
depend on soil buffering capacity and inherent N mineralization potential. Redistribution and mixing
of nutrients varies with the degree of soil mixing so the choice of CT system and duration of CT
practice will depend on native soil fertility and the resistance of soil to chemical change.
INVASIVE SPECIES
According to the Convention on Biological Diversity (CBD), “Invasive alien species are
species introduced deliberately or unintentionally outside their natural habitats where they have the
ability to establish themselves, invade, out compete natives and take over the new environments”.
They are widespread in the world and are found in all categories of living organisms and all types of
ecosystems. However, plants, mammals and insects comprise the most common types of invasive alien
species in terrestrial environments (Catindig JL & Heong K H, 2006).
In the Philippines, four of the most important alien invasive pests are the golden apple snail,
locally known as golden kuhol (Pomacea canaliculata (Lamarck)), the rice black bug, locally known as
“itim na atangya” (Scotinophara coarctata (Fabricius)), the mango pulp weevil (Sternochetus frigidus
(Fabricius)) and the mango seed weevil (S. mangiferae (Fabricius)).
The golden apple snail and the rice black bug feed on rice. Rice, the food crop for more than
half the world’s population is the staple food in the Philippines. Of the 4 million hectares of total rice
area, the average rice yield in the Philippines as of 2000 was 3.1 metric tons (MT) per hectare (IRRI,
2002).
The mango pulp weevil, Sternochetus frigidus (Fabricius) and the mango seed weevil, S.
mangiferae (Fabricius) attacked mango fruits of cultivated and wild species in some parts of Asia like
the Philippines (Gabriel, 1977; De Jesus, et al., 2004). Mango is the national fruit in the Philippines
and is the third most important fruit crop of the country based on export volume and value next to
banana and pineapple. Mango export in the country reached to 35,771 MT in 2003 ($31.011 million)
with country’s production of close to one million metric tons (http://www.mb.com.ph).
RICE PRODUCTION IN WATER-SCARCE ENVIRONMENTS
Procedure for composite sampling
1. Present to the inspector the production documents containing the number of containers per
batch number and container number.
2. The inspector will randomly select the container number and subject the selected containers
for analysis.
60
3. Information relative to the sample taken must be accurate and complete to allow traceability of
the sample back to the lot from which it was sampled.
4. Organic Fertilizer.
Production of staple food crops, such as rice and maize, to compensate the growth of the
population has become a major challenge for many developing countries. To cope with the
encountered problems, either crop production or management of land has to be improved.
Management of land by introducing of organic inputs, such as pruning and crop residues, and
utilization of new agricultural resources has to be considered.
Productive irrigated areas in Indonesia are estimated to decrease by 30,000 - 40,000 ha
annually due to industrial development and settlement. Consequently, it becomes necessary to utilize
other agricultural resources to increase crop production. Despite the increase in area planted of Rainier
lowland rice, the yields remain low due to the low soil fertility and the lack of infrastructure and water
resources. Improvement of Rainier lowland management is therefore needed in order to increase yields.
Rain field paddy field ecosystem is found widespread in Asia.This system is not irrigated and
therefore depends on rainfall. The water is impounded by bunds and water-depth may exceed 50 cm.
No additional water is supplemented. Rain field paddy field system is characterized by lack of water
control, with floods and drought being potential problems. This system consisted of three different
planting seasons per year, i.e. rice planting in the beginning of rainy season, upland crop planting in
the end of rainy season and after the harvest of crop the field is left fallow during the dry season.
Therefore, the Rain field paddy field system undergoes two different systems, i.e. flooded and dry
system. Consequently, the population and diversity of soil fauna, organic matter, and nitrogen turnover are different in those systems.
Little is known about the influence of the dynamics of soil fauna on organic matter
decomposition in Rain field paddy field system. Therefore, the study of environmental changes is
important to optimalize organic matter decomposition and nitrogen turn-over of the system.
Tubificidae are key component of the soil fauna in wetland rice fields. Their major role regarding soil
fertility is the trans location of components of photosynthetic aquatic biomass from the surface to the
deeper soil layer. The breakdown products of photosynthetic biomass contribute to the replenishment
of soil microbial biomass and the provision of nutrients to the rice plant.
CROP/SOIL
MANAGEMENT
PRACTICES
TO
MAINTAIN
OR
IMPROVE
SOIL
PRODUCTIVITY
To maintain or improve the productivity of soils used for cassava cultivation, it is necessary to
reduce nutrient losses by crop removal and erosion, and prevent physical deterioration through
61
excessive land preparation (especially with heavy machinery), and loss of clay and organic matter
through erosion. In addition, the nutrients and organic matter lost should be replaced by application of
fertilizer or manures, or by incorporation of green manures or inter crop residues.
Fertility Maintenance
The decline in soil fertility due to cassava cultivation can be partially prevented by reincorporation into the soil of all above-ground parts of the cassava plant, such as stems, leaves and
fallen leaves, removing from the field only the roots. Long-term NPK trials conducted on a very poor
soil show that without fertilizer application but with incorporation of plant tops, yields of about 12 t/ha
could be maintained after more than 15 years of continuous cropping, while yields decreased to 5-7
t/ha when plant tops were also removed from the field.
Chemical fertilizers
Nutrients removed in harvested products, in runoff and eroded sediments can be replaced by
application of chemical fertilizers. Moreover, although cassava can grow on poor soils, the crop is
highly responsive to fertilizer applications. While in most cases there is a yield response only to the
application of N, P and K, in some cases, especially if plant tops are also removed, there may also be a
yield response to the secondary (Ca, Mg, S) and micro-nutrients (especially Zn).
Numerous long-term fertility trials conducted in 11 locations in Asia indicate that after 4-10
years of continuous cassava cultivation, there were significant responses to application of N in 8, to K
in 7 and to P in 4 of 11 locations. Thus, in most cassava growing soils in Asia, there is mainly a
response to application of N and K, and only in a few areas is there also a response to P.
Nutrient concentrations in plant tissues vary continuously during the crop cycle and are very
different for different plant parts (leaves, petioles, stems) and location within the plant (upper, middle
or lower part). For that reason, for diagnostic purposes, only the “indicator” tissue, i.e. the youngest
fully-expanded leaf (YFEL) blades (without petioles), are collected at 3-4 months after planting (if in
the wet season); these samples are quickly dried in the sun or in an oven at 60-80oC for 1-2 days; after
grinding in a mill they are sent to the laboratory for analysis.
In the absence of laboratory facilities, a rough estimate of nutritional requirements can also be
obtained from simple trials on farmers’ fields using three rows each of the following treatments:
N0P0K0, N0P1K1, N1P0K1, N1P1K0, and N1P1K1, where N0, P0, K0 indicate without N, P or K,
and N1, P1, K1 correspond to about 100 kg N, 40 P2O5 and 100 K2O/ha, respectively, using urea,
62
SSP and KCl as the nutrient sources; animal manures should not be applied in these trials. The yields
of the center row of each treatment will give an indication of the relative importance of the three
nutrients, after which more detailed trials can be conducted to determine the optimum amount(s) of the
most important nutrient(s).
ORGANIC MANURES
The nutrient contents of these manures are seldom known and are highly variable. On average,
chicken manure seem to be relatively high in N, K, Ca and Mg, while pig manure is relatively high in
P. Wood ash, water hyacinth and rice husks are all good sources of K, while wood ash is also very
high in Ca and Mg. Manures are thus a major and indispensable source of nutrients for cassava, while
also contributing organic matter and improving the physical conditions of the soil. These manure
applications are particularly important when farmers remove all plant parts from the field, as they help
restore soil organic matter and supply secondary and micro nutrients.
GREEN MANURES AND ALLEY CROPPING
Few experiments have been conducted to determine the effectiveness of planting and then
incorporating a crop of green manure before planting cassava. In areas where farm size is small, few
farmers will want to plant a non-productive crop for the sole purpose of improving soil fertility.
However, in remote areas where land is abundant but fertilizers or manures are not available, this may
be an attractive option. Moreover, the green manure may help to smother out Imperata cylindrica
grass.
Experiments with various green manure species conducted showed that incorporation of
Crotalaria juncea, Canavalia ensiformis, Mucuna sp and pigeon pea increased cassava yields when no
fertilizers were applied, but had no significant effect on yield in the presence of fertilizers.
Alley cropping cassava with contour hedgerows of Tephrosia candida is a well-established
practice in some parts of north Vietnam. It is used to control erosion as well as to improve soil
fertility when the prunings of the hedgerows are mulched or incorporated.
INTERCROPPING
Trials conducted for four years indicate that inter cropping cassava with grain legumes, such
as mungbean, soybean, cowpea, peanut, winged bean (Psophocarpus tetragonolobus) and sword bean
(Canavalia ensiformis) decreased cassava yields about 10-20%, and that planting cassava in single
rows at 1.0x1.0 m produced higher yields than planting in double rows. inter cropping with maize also
63
reduced cassava yields about 20-25%. Profits were highest for cassava monoculture or inter cropping
with peanut (Nguyen Huu Hy et al., 1995).
When cassava was grown on 9-12% slope, inter cropping with peanut and planting hedgerows
of Tephrosia candida, reduced soil losses and runoff, especially when managed with high inputs of
fertilizers. inter cropping and hedgerows reduced cassava yields, but the additional income from the
peanut more than compensated for the lower income from cassava. inter cropping with peanut
generally produced higher net income for the farmer than inter cropping with other crops or mono
cropping.
EROSION CONTROL
Numerous erosion control trials conducted have shown that runoff and erosion losses can be
markedly reduced by inter cropping and planting of contour hedgerows. inter cropping with peanut
was generally more effective in reducing erosion than inter cropping with other crops, due to the rapid
formation of soil cover. Contour ridging and no- or reduced tillage were also effective in reducing
erosion, while adequate fertilization also helped to reduce erosion.
However, contour ridging,
fertilization and inter cropping require more work and usually imply higher production costs.
Hedgerows also require more work in establishment and maintenance and may reduce yields by
occupying 10-20% of the land. Thus, farmers have to consider the trade-off between immediate costs
and benefits versus long-term benefits of less erosion and improved fertility.
TRANSFER OF TECHNOLOGIES
While many management practices to control erosion have been recommended by researchers
and extension agents, few of these practices have actually been adopted by farmers. This is mainly
because most of the recommended practices require either additional labor or money, and benefits are
usually accrued over the long-term, while most poor cassava farmers are in desperate need of
immediate income to feed their families.
The NPV for the first two years was very low due to the high initial costs of establishing the
hedgerows, the costs of maintenance and the lower maize yields obtained. Thus, the farmer will not
receive economic benefits from planting hedgerows until after about five years. It is only after 10-15
years that farmers will reap substantial economic benefits from these soil erosion practices, but that is
too long for most farmers with a short planning horizon, or with immediate needs for adequate income.
This example shows the main dilemma in promoting soil conservation practices: most recommended
practices were selected by researchers because they are effective in controlling erosion, but few
consider whether poor farmers can actually bear the economic burden of adopting these practices. If
64
they can not, governments may have to provide some incentives, since part of the benefits of better
erosion control are reaped off-site by people living downstream or in the cities.
Another problem in the transfer of soil conservation technologies is that many soil erosion
control trials were conducted on experiment stations under optimum and uniform conditions. These
conditions seldom correspond with those faced by farmers living in mountainous areas with
heterogeneous soils, topography and climates, and with economic opportunities that vary markedly
from place to place depending on distance to roads and markets. Many practices that seemed very
effective in controlling erosion, and may have economic benefits under the conditions of the
experiment station, may be rejected by farmers simply because they are not effective or not
appropriate under the farmer’s specific biophysical and socioeconomic conditions. For that reason it
is more effective to present farmers with a range of options, from which they can select those that they
consider useful, and let them try out some of these options on their own fields; this way farmers can
observe and decide which is the most effective and useful practice for their own conditions. This
farmer participatory research (FPR) methodology is particularly useful for developing and
disseminating technologies like erosion control practices, that are highly site-specific and where there
are many trade-offs between costs and benefits. Only farmers themselves can decide about the costs
they can bear and the risks they can take now in order to obtain benefits sometime in the future.
Some erosion control practices, such as inter cropping with peanut, application of fertilizers
and contour hedgerows of vetiver grass or Tephrosia candida can reduce soil loss to about one third,
while doubling gross and net income. These were the practices most farmers selected as most useful
for their particular conditions. Farmers selected a combination of practices, like new varieties, better
fertilization, inter cropping etc. that increased income, in combination with contour hedgerows that
mainly reduced erosion, so as to obtain both short-term and long-term benefits.
The past years have seen a growing scarcity of water worldwide. The pressure to reduce water
use in irrigated agriculture is mounting, especially in Asia where it accounts for 90% of total diverted
fresh water. Rice is an obvious target for water conservation: it is grown on more than 30% of
irrigated land and accounts for 50% of irrigation water. Reducing water input in rice production can
have high societal and environmental impact if the water saved can be diverted to areas where
competition is high.
However, rice is very sensitive to water stress. Attempts to reduce water in rice production
may result in yield reduction and may threaten food security in Asia. Reducing water input for rice
will change the soil from submergence to greater aeration. These shifts may have profound – and
largely unknown – effects on the sustainability of the lowland rice ecosystem. Our challenge is to
develop socially acceptable, economically viable, and environmentally sustainable novel rice-based
systems that allow rice production to be maintained or increased in the face of declining water
65
availability. This paper reviews the status of water resources in rice growing areas and the
opportunities and challenges of growing more rice with less water.
WATER RESOURCES IN RICE-GROWING AREAS
Rice can be grown under irrigated (lowland) or Rain field (upland or lowland) conditions.
Rain field rice occupies about 45% of the global rice area and accounts for about 25% of the rice
production. Drought has been identified as one of the main constraints for improving yield, which
presently averages 2.3 t ha.1. According to Garrity et al. (1986), 50% of Rain field lowland and all
Rain field uplands are drought prone. Severe and mild droughts often occur in predominantly Rain
field rice areas.
More than 75% of rice supply comes from 79 million ha of irrigated lowlands. Most of the
approximately 22 million ha dry season irrigated rice areas in South and Southeast Asia falls in the
“economic water scarcity” zone. However, there may be an over estimation of the water availability in
the dry season, because IWMI’s water scarcity calculations are based on the annual water balance. In
principle, water is always scarce in the dry season when the lack of rainfall makes cropping impossible
without irrigation. Thus, there may be rice areas in the “economic water scarcity” zone affected by
“physical water scarcity” in the dry season.
Heavy upstream water use along some major rivers in Asia is causing severe water shortages
downstream. Irrigated rice production is also increasingly facing competition from other sectors.
Water from the Angat reservoir in Bulacan Province, the Philippines, is increasingly diverted toward
Manila at the expense of downstream water availability for agriculture.
Lowland rice in Asia is mostly transplanted or direct (wet) seeded into puddled, lowland
paddy fields. Land preparation of a paddy consists of soaking, plowing and puddling. Puddling is
mainly done for weed control, but also increases water retention, reduces soil permeability, and eases
field leveling and transplanting. Soaking is a one-time operation and requires water to bring the topsoil
to saturation and to create a ponded water layer. There are often “idle periods” in between tillage
operations and transplanting, prolonging the land preparation period up to 1 to 2 months in large-scale
irrigation systems (Tuong, 1999). The crop growth period runs from transplanting to harvest. During
this period, fields are flooded with typically 5-10 cm water until final drainage some 10 days before
harvest.
Under flooded conditions, water is required to match outflows (seepage, S, and percolation, P)
to the surroundings and depletions to the atmosphere (evaporation, E, and transpiration, T). The flow
rates of S and P are governed by the water head (depth of ponded water) on the field and the resistance
to water movement in the soil. Because they are difficult to separate in the field, S and P are often
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taken together as one term, i.e., SP. SP can be as high as 25 mm d-1 during land preparation, because
soil cracks do not close completely during land soaking (Tuong et al, 1996).
The water input in paddy fields depends on the rates of the outflow processes and on the
duration of land preparation and crop growth. For a typical 100-d season of modern high yielding rice,
the total water input varies from 700 to 5300 mm, depending on climate, soil characteristics and
horological conditions with 1000-2000 mm as a typical value for many lowland areas. Of all outflows
of water from a paddy field, only transpiration is “productive” water use since it leads directly to crop
growth and yield formation. Most of the water input to a rice field, however, is to compensate for
evaporation during land preparation and SP during land preparation and the crop growth period. These
flows are unproductive as they do not contribute to crop growth and yield formation.
WATER PRODUCTIVITY
Water productivity is the amount of grain yield obtained per unit water. Depending on the type
of water flows considered, water productivity can be defined as grain yield per unit water
evapotranspired (WPET) or grain yield per unit total water input (irrigation plus rainfall) (WPIP). At
the field level, WPET values under typical lowland conditions range from 0.4 to 1.6 g kg-1 and WPIP
values from 0.20 to 1.1 g kg-1 (Tuong, 1999). The wide range of WPET reflects the large variation in
rice yield as well as in evapotranspiration caused by differences in environmental conditions under
which rice is grown. However, WPIP of rice is about less than 50% of that of wheat. The relatively
low WPIP of rice is largely due to the high unproductive outflows discussed above (SP and E).
Beside the yield and the size of field-level water outflows, the scale and the boundary of the
area over which water productivity is calculated greatly affects its value. This is because the outflow
“losses” by seepage, percolation and runoff at a specific location (or field) can be re-used at another
location within the area under consideration. Data on water productivity across scales are useful
parameters to assess if water outflows upstream are effectively re-used downstream. The paucity of
water productivity data at scale levels higher than the field reflect the lack of (i) data on water flows or
yield, or both, at the such scales and (ii) the cooperation between those who work in agriculture (who
may have production data) and those who work in the “water management” sector (who may have
water flow data).
Increasing water productivity can be accomplished by (i) increasing the yield per unit ET
during crop growth, (ii) reducing the unproductive water outflows and depletions (SP, E), or (iii)
making more effective use of rainfall. The last strategy is important from the economic and
environmental point of view where the water that needs to be provided through irrigation can be offset
by that supplied by rainfall, or replaced entirely by rainfall.
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GERMPLASM DEVELOPMENT AND AGRONOMIC PRACTICES
Germplasm development has played an important role in increasing water productivity in rice
production. By increasing yield and simultaneously reducing crop duration (and therefore the outflows
of evapotranspiration, seepage and percolation), the modern “IRRI varieties” have about 3-fold
increase in water productivity compared with the traditional varieties. Most of the increase in WPET,
however, occurred in cultivars released before 1980 (Tuong, 1999).
In the low fertility, drought-prone Rain field environments, breeders have been most
successful in manipulating drought escape. Exposure to drought is minimized by reducing crop
duration or by minimizing the risk of coincidence of sensitive crop stages with water-deficit periods.
The progress in breeding for drought tolerance is less spectacular, and is often blamed on the genetic
complexity of the trait and its interaction with the environment. Nevertheless, drought-resistant
varieties are being bred and released in upland and drought-prone Rain field lowland areas. Salinitytolerant varieties, such as Ir51500-AC11-1, allow us to grow rice in areas where salinity problems
exclude the cultivation of conventional lowland varieties.
Improved agronomic practices, such as site-specific nutrient management, good weed
management and proper land leveling can increase rice yield significantly without affecting ET, and,
therefore, may result in increased water productivity.
In transplanted rice, seedlings are usually nurtured in a seedbed for about 2-4 weeks. In
irrigation systems that lack tertiary and field channels, and with field-to-field irrigation, all the fields
surrounding the seedbeds are being tilled (land preparation) and flooded during this period. This land
preparation period can be shortened by the provision of tertiary infrastructure to (i) supply irrigation
water directly to the nurseries without having to submerge the main fields, and (ii) to allow farmers to
carry out their farming activities independently of the surrounding fields (Tuong 1999).
Another way to reduce the idle period during land preparation in irrigation systems without
tertiary canals is the use of direct seeding (Tuong et al., 1999). However, the crop growth period in the
main field of transplanted rice is shorter than that of direct-seeded rice. Thus, the amount of water
saved by direct seeding depends on the balance between the reduction in water use caused by
shortened land preparation and the increase in water use caused by prolonged crop growth duration in
the main field (after crop establishment, Cabangon et al., 2001).
The resistance to water flow can be increased by changing the soil physical properties.
Cabangong and Tuong (2000) showed the beneficial effects of an additional shallow soil tillage before
land preparation to close cracks that cause rapid bypass flow at land soaking. However effective,
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though, soil compaction and physical barriers are expensive and beyond the financial scope of most
farmers.
USING RAINFALL MORE EFFECTIVELY
Dry-seeded rice technology offers a significant opportunity for conserving irrigation water by
using rainfall more effectively. In transplanted and wet-seeded rice systems, farmers normally wait for
delivery of canal water before they start land soaking. In dry-seeded rice, land preparation is done with
dry or moist soil conditions and is started using early monsoon rainfall. Crop emergence and early
growth also occur in the early part of the monsoon, and only later, when canal water is available, is the
crop irrigated as needed.
Cabangon et al. (2001) reported that dry-seeded rice significantly increased water productivity
with respect to irrigation water over wet-seeded and transplanted rice in the Muda irrigation Scheme,
Malaysia. However, it was also observed that all three crop establishment practices had similar total
water input and water productivity with respect to total water input. An additional advantage of dry
seeding is the early establishment of the crop which may allow farmers to grow an extra crop after
harvest on residual soil moisture (My et al., 1995; Saleh et al., 1995) or using saved irrigation water.
In purely Rain field systems, early establishment and harvest of dry-seeded rice allows the rice plants
to escape any late season drought and hence improve the yield and its reliability.
EMERGING APPROACHES
Raised beds for saturated soil culture
Implementing SSC requires good water control at the field level, and frequent, shallow
irrigations that are labor intensive. The benefits of growing rice on raised beds with SSC may be
extended to a post-rice crop, such as wheat in the rice-wheat system. The productivity of crops sown
after rice is often low due to poor soil physical structure and water logging from winter rainfall and
spring irrigation. A bed system may improve drainage conditions for a post-rice crop.
AEROBIC RICE
A fundamental approach to reduce water inputs in rice is to grow the crop like an irrigated
upland crop such as wheat or maize. Instead of trying to reduce water input in lowland paddy fields,
the concept of having the field flooded or saturated is abandoned altogether. Upland crops are grown
in non-puddled, aerobic soil without standing water. Irrigation is applied to bring the soil water
content in the root zone up to field capacity after it has reached a certain lower threshold. The amount
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of irrigation water should match evaporation from the soil and transpiration by the crop (plus any
application inefficiency losses).
New varieties must be developed if the concept of growing rice like an irrigated upland crop is
to be successful. Upland rice varieties exist, but have been developed to give stable though low yields
in adverse environments where rainfall is low, irrigation is absent, soils are poor or toxic, weed
pressure is high and farmers are too poor to supply high inputs.
BIOTECHNOLOGY
The recent advancement in genomics, the development of advanced analytical tools at the
molecular level, and genetic engineering provide new avenues for raising the yield potential and
enhancing drought stress tolerance. The currently slow progress in breeding for drought tolerance may
be accelerated by discovery and subsequent manipulation of regulatory genes underlying the complex
physiological and biochemical responses of rice plants to water deficit. Common research tools,
tolerance mechanisms and breeding solutions are emerging across the evolutionary diversity of crops
plants.
OPPORTUNITIES AND CHALLENGES IN WATER-SAVING PRACTICES
Growing rice in continuously flooded fields has been taken for granted for centuries, but the
“looming water crisis” may change the way rice is produced in the future. The basic ingredients of
implementing these technologies seem to be in place. But so far, the adoption of these technologies
has been slow. The challenge is to identify the environmental and socioeconomic conditions that
encourage farmers to adopt them. In this respect, our research is far from complete. We can, however,
identify important factors that affect the farmers’ acceptance of water saving technologies.
Unlike fertilizers and pesticides, water is generally not actively traded on markets in Asia, and
government-administered fees for irrigation water are often low or zero. This discourages farmers
from treating water as a scarce resource. Farmers have no incentive to adopt water-saving technologies
because water conservation does not reduce the farming expenditures nor does it increase income. It
can be expected that when water becomes a real economic goods, farmers are more inclined to adopt
water-saving technologies. There is evidence that farmers in Asia that are confronted with high costs
of water already adopt such technologies.
Water-saving technologies that improve productivity and income will be easily accepted by
farmers. Dry seeding is widely practiced in drought-prone Rain field systems because of its ability to
increase rice yield and its stability and cropping intensity. In irrigated systems, however, water-saving
technologies are mostly associated with some reduction in yield. Technologies that save water for rice
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and increase productivity of a post-rice crop will be more acceptable to farmers. The prospect of raised
bed to increase the total system productivity of the rice-wheat system opens up opportunities to save
water. Similarly, farmers may accept dry-seeding technologies in irrigated system to reduce the labor
cost of transplanting and wet land preparation.
All water-saving technologies, from SSC to ADW to dry seeding and aerobic rice, reduce
water depth and expose rice fields to periods without standing water. Poor leveling of rice fields is
common in Asia, leading to heterogeneity in the depth of standing water. This will result in a more
competitive and diverse weed flora than in rice under conventional water management. On-farm
research has shown that precise land leveling can improve the establishment of direct-seeded rice and
increase water productivity. Improving farmers’ knowledge on improved (integrated) weed
management will enhance their acceptance of water-saving technologies.
Suitable policies, institutional organization and legislation are needed to promote the adoption
of water-saving technologies. The establishment of water user groups and the implementation of
volumetric water charging may be the most important elements behind the successful adoption of
AWD in China. New laws prohibiting flooded rice cultivation in parts of Shandong province and
around Beijing is expected to increase farmer’s interest in aerobic rice cultivation.
Soil submergence is a unique feature of irrigated lowland rice ecosystems. Lowlands
producing two or three rice crops per year on submerged soils are highly sustainable, as indicated by
sustained nutrient supply capacity, sustained soil carbon levels, and sustained trends in rice yields.
However, the continuous submergence of soil promotes the production of methane, an important
greenhouse gas, by the anaerobic decomposition of organic matter. Temporary soil aeration, such as
under AWD, can reduce methane emission. Prolonged aeration of soil, such as in aerobic rice, can
even reduce methane emission further. Soil aeration, on the other hand, can increase the emission of
nitrous oxide, another greenhouse gas. Emissions of methane and nitrous oxide are strongly related to
the soil redox potential, a measure of soil oxidation status. Both methane and nitrous oxide emissions
could be minimized by maintaining the soil redox potential within a range of –100 to +200 mV. An
important research area is to assess whether water-saving technologies can achieve such an
intermediate soil redox potential (Powlson, DS and Olk, D; 2000).
Increased soil aeration under AWD and in aerobic rice will also affect the soil organic matter
status and the soil nutrient supply capacity. It could also pose challenges for managing crop residues.
The more competitive weed flora associated with water-saving technologies may require a greater
reliance on herbicides, which challenges environmental sustainability. Critical issues for water-saving
technologies may include how much water and how frequent soil submergence is required for
sustaining the productivity and services of rice ecosystems.
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The impact of on-farm water saving on the role of water in sustaining the environmental health
warrants further investigation. In many basins, the drainage and percolation outflows from rice fields
return to the lower reaches of the rivers. They play an important environmental role in sustaining the
fresh – saline water balance in estuaries. Reducing the outflows may results in increased salinity
intrusion. The drying up of the lower reaches of rivers and declining water tables indicate that, in such
areas, all the utilizable outflows from upstream have been re-used. Water-saving practices that aim to
reduce the drainage and percolation outflows from paddies, are important options for farmers to
maintain rice cultivation in the face of water scarcity, but they may not increase water availability of
the whole basin.
RICE-WHEAT CROPPING SYSTEMS IN WATER PRODUCTIVITY IN RELATION TO
NEW RESOURCE CONSERVING TECHNOLOGIES.
The rice-wheat cropping system is found on 13.5 million hectares in South Asia and is one of
the most important cropping patterns for food self security in the region. Both crops are grown in one
calendar year. Other crops, particularly in the winter, are also grown including pulses, oil seeds,
potatoes, vegetables, fodders and sugarcane. Irrigation is a common feature of this system either from
extensive surface canal systems or from shallow wells and tube wells (shallow or deep). Rain field
rice-wheat also exists, but the majority of farmers apply at least one irrigation for wheat and many a
full irrigation schedule (Dobermann, A., & Fairhurst, T., 2000).
During the past 30 years, agricultural production has been able to keep pace with population
demand for food. This came about through significant area and yield growth. Area growth was a result
of new lands being farmed and through increases in cropping intensity, from a single crop to double or
even triple crops per calendar year. Area growth will be less important in its contribution to production
growth in the future as more land is used for urban areas and industry. Yield growth will have to be
the mainstay for providing the means for meeting future food demands unless food imports start to
play a major role in South Asia. Evidence from some long-term experiments, however, show that
problems of stagnating yields at levels far below the potential productivity and even yield declines are
occurring in some areas in the rice-wheat systems of South Asia. Total factor productivity is declining
and farmers have to apply more fertilizer to obtain the same yields. Soil organic matter is declining,
new weeds, pest and diseases are creating more problems, and paucity of irrigation water in northwest
is resulting in excessive ground water pumping. Farmers are complaining about high input costs and
low prices for their produce. Marketing of excess production is a burden for farmers and a problem to
governments for storage. There is therefore a huge challenge ahead in the region to sustainability meet
future food demands without damaging the natural resource base on which agriculture depends,
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producing food at a cost that is affordable by the poor, and with incentives to farmers that allow them
to improve their livelihoods and ultimately alleviate poverty.
REDUCED TILLAGE
The Chinese have developed a seeder for their 12 horsepower, two-wheel diesel tractor that
prepares the soil and plants the seed in one operation. This system consists of a shallow rotovator
followed by a six-row seeding system and a roller for compaction of the soil.
The rotovator fluffs up the soil, which then dries out faster than with normal land preparation.
The seeding coulter does not place the seed very deep, so soil moisture must be high during seeding to
ensure germination and root extension before the soil dries appreciably. Modification of the seed
coulter to place the seed a little deeper would help correct this problem.
The main drawback of this technology is that the tractor and the various implements are not
easily available and spare parts and maintenance is major issue. It would help if the private or public
sector in South Asian countries could import this machinery or develop a local manufacturing
capability. As it becomes more costly to keep and feed a pair of bullocks for a year, more farmers in
the region are turning to significantly cheaper mechanized options of land preparation. One of the
benefits of this tractor is that it comes with many options for other farm operations; it includes a reaper,
rotary tiller, and a moldboard plough, and it can also drive a mechanical thresher, winnowing fan, or
power source for pumping water. However, most farmers are attracted to the tractor because it can be
hitched up to a trailer and used for transportation. For smaller-scale farmers who cannot afford their
own tractors, custom hiring is a common alternative.
BED PLANTING SYSTEMS
In bed planting systems, wheat or other crops are planted on raised beds. Farmers have given
the following reasons for adopting the new system:
1.
Management of irrigation water is improved.
2.
Bed planting facilitates irrigation before seeding and thus provides an opportunity
for weed control prior to planting.
3.
Plant stands are better.
4.
Weeds can be controlled mechanically, between the beds, early in the crop cycle.
5.
Wheat seed rates are lower.
6.
After wheat is harvested and straw is burned, the beds are reshaped for planting
the succeeding soybean crop. Burning can also be eliminated.
7.
Herbicide dependence is reduced, and hand weeding and rouging is easier.
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8.
Less lodging occurs.
This system is now being assessed for suitability in the Asian Subcontinent. The major weed
species affecting wheat, Phalaris minor, is normally controlled using the herbicide Isoproturon, which
is not always effective. Farmers do not always apply Isoproturon well or on time; in addition, recent
reports have confirmed that P. minor has developed Isoproturon resistance. Alternative integrated
weed strategies must be developed to overcome this problem. Preliminary observations indicate that P.
minor is less prolific on dry tops of raised beds than on the wetter soil found in conventional flat bed
planting. Cultivating between the beds can also reduce weeds. Thus bed planting provides farmers
with additional options for controlling weeds.
Lodging is also less of a problem on raised beds. Additional light enters the canopy and
strengthens the straw, and the soil around the base of the plant is drier. Reduced lodging can have a
significant effect on yield, since many farmers in the Punjab do not irrigate after heading precisely
because they want to avoid lodging. As a result, water can become limiting during grain filling,
resulting in lower yields. On raised beds this irrigation need not be avoided for the reasons stated.
Results show that there are no significant difference between flat and bed planted systems,
which means that yield was not sacrificed by moving to a bed system. Upright varieties such as HD
2329 perform poorly on beds and cannot compensate for the gap between the beds.
An additional advantage of bed planting becomes apparent when beds are “permanent” – that
is, when they are maintained over the medium term and not broken down and re-formed for every crop.
In this system, wheat is harvested and straw is left or burnt. Passing a shovel down the furrows
reshapes the beds. The next crop (soybean, maize, sunflower, cotton, etc.) can then be planted into the
stubble in the same bed. Research in farmer fields has also shown that rice can be grown on beds
making this system feasibility in the rice-wheat pattern. Rice can be grown on beds by either
transplanting seedlings or direct seeded. At the moment, transplanting on beds is best since normal
herbicides used for transplanted rice can be used to control weeds. As dry seeded herbicides become
available and weeds can be managed, dry seeded rice on beds will become more attractive.
The use of beds also provides a way for improving fertilizer use efficiency. This is achieved
by placing a band of fertilizer in the bed at planting or topdress. Using slow release formulations and
experimenting with urea super granules can make further improvements. Both can be applied in the
bed at the time of planting with the seed cum fertilizer drill.
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MULTI USE OF LOW QUALITY WATER
Low quality waters are often used in cyclic mode in the Indo-Gangetic plains. At times they
are blended with canal water in watercourses to improve the total water supply and also the flow rates.
Blending of low and good quality waters have earlier been discouraged because of their adverse effect
on crop productivity. However, if the resultant electrical conductivity of the blended water supplies is
less than the threshold conductivity, they can be used safely. In combination with new RCTs, blending
of multi-quality water supplies in on-farm water storage reservoirs not only improves the quality of
waters having residual sodium carbonates and overcome problems associated with this water, but can
also improve the use of rainwater and water productivity and yields of a bed planted wheat crop.
Preliminary results of a trial conducted in Pakistan have been very encouraging. Bed planting system
also offers scope for use of even saline waters. When saline waters are applied in raised bed-furrow
land configuration, it permits salt movement to the top of the raised beds keeping the rootzone
relatively free of salts below the furrow. This improves the ability of the plants to avoid early salt
injury at seedling stage and subsequently improve salt tolerance of the crop due to crop ontogeny. Bed
planting when combined with mulching or residue retention has the potential to reduce evaporation
losses from the soil surface, salinization and further improve crop productivity in saline environments.
NON-PUDDLING FOR RICE
The benefits of the new resource conserving tillage options listed above are lost when rice
soils are puddle (ploughed when wet). The RWC is therefore encouraging research on-station and with
farmers to find ways to eliminate this soil degrading process. Most rice farmers in South Asia
traditionally puddle their soils to help pond water, reduce percolation losses and control weeds. Initial
data indicates that rice fields do not need to be flooded after the first few weeks and that puddled soils
have more cracking and need more water once the fields dry. Initial flooding though is important to
promote tillering and to more effectively control weeds. Studies are also being initiated to determine
the exact water balance for the puddled and non-puddled conditions at the field, water course and
command level. This is being done for fields where bed planting is practiced and in fields with flat
planting, with and without tillage. As mentioned above, farmers feel that bed planted rice saves water
over the traditional system.
All the above technologies can benefit from levelled fields. However, when this is combined
with 0-tillage, bed planting and non-puddled rice culture, plant stands are better, growth is more
uniform and yields higher. Use of permanent bed systems and 0-tillage results in less soil disturbance
and reduces the need for future labelling.
Farmers also report water savings in bed planting. Farmers commonly mention 30-50%
savings in this system. Farmers also indicate that it is easier to irrigate with bed planting. Obviously,
half the space is used for water and so less water is used. The question is whether farmers need to
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apply more number of irrigations with this system. In the initial year of planting rice on beds, farmers
estimated they used 50-65% less water than on the flat. They kept the beds flooded for the first week,
but were then able to cut down on irrigation frequency later. This also needs to be confirmed with
good quantitative data.
We still need to collect the data for the water use under puddled and non-puddled rice
cultivation. Definitely, water percolation will be higher in non-puddled situations, but the total water
use may be less since no water is needed for seedling raising or puddling the main field. Also when
puddled soils dry, and many farmers cannot keep their fields continuously flooded, soils crack and so
the field needs more water to fill the profile when water is next added. Less cracking occurs in nonpuddled soils. Data is also being accumulated that the rice crop does not need to be kept flooded the
whole season. Standing water is needed early to help tillering and control weeds, but later this is not
required.
IMPORTANCE OF PARTICIPATORY TECHNOLOGY DEVELOPMENT
Adoption of RCTs in South Asia has been rapid over the past few years, especially for 0-till
with the inverted-T planter. This success was possible because of the application of participatory
approaches for accelerating adoption. The traditional extension system that was so effective in the
early years of the GR was based on development of recommendations and packages and then having
the extension service demonstrate the technology to farmers. Seed and fertilizer was easily packaged
and it was possible to layout many trials at low cost. When this traditional extension system was used
for extending RCTs, problems arose. The first problem was the availability of the machinery to
conduct the demonstrations. However, the main constraint was convincing farmers, extension workers
and at times scientists that this technology had any benefit. Success came once partners were allowed
to work together and experiment with the technology. Local manufacturers had to be involved in the
development and manufacture of the equipment. Machinery had to be of high quality, yet at a cost
within the budgets of farmers. Farmers had to be shown how the drill worked and then allowed to
experiment with the equipment, before he could be convinced to accept this radical technology.
One question that is often asked is “who can benefit from this technology? Is it just for the
large, commercial farmer?” The answer appears to indicate that this technology is scale neutral and
that farmers from all social classes can benefit from the many advantages that this system brings to
wheat cultivation.
When this is applied to 0-till or bed planting, the benefits are even more pronounced. In this
case, the farmer has only to rent the service once and his fields are planted. This saves him money and
time to do other activities. Data from socioeconomic and impact assessment surveys in India and
Pakistan show this to be true. The first innovators are larger, better endowed, tractor owners. Later less
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endowed farmers adopt the technology as they see the benefits and obtain the services for this
technology.
Farmer responses and feed back to the RCT’s and especially 0-tillage provide valuable
feedback to scientists in the RWC for improving the technology. At the same time, scientists have
been monitoring the fields where these technologies are being adopted and collecting data on soil,
biotic, and resource use.
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III. BIO-INTENSIVE GARDENING AND OTHER COMPOSTING METHODS
BIODIVERSITY-BASED FARMING SYSTEMS IN THE PHILIPPINES
For centuries, farming communities have painstakingly developed resilient and bountiful
agricultural systems based on biodiversity, and on their knowledge of how to work with them in
equally complex biophysical and socio-cultural settings. Farmers have used diversity for food and
economic security through a complex array of home garden designs, agroforestry systems and
diversified and integrated lowland farming systems. It differs substantially from conventional modern
agriculture in that its focus is the establishment of functional diversity in the farm, rather than monopoverty in that area (Bachmann, L., Cruzada, E., & Wright, S., 2009).
These systems are time-tested and locally adapted. Principles to be considered in the practice
of DIFS are biodiversity, nutrient cycling and management, appropriate pest management, adapted
animal breed or crop variety, and soil and water management.
One of the most stable, productive and profitable diversified cropping systems in the
Philippines is the coconut-based multi-storey system developed and practiced in Cavite. Other case
examples are organic farming as practiced by small-scale farmers of MASIPAG, the bio-intensive
gardening (BIG) promoted by the International Institute of Rural Reconstruction (IIRR) in Cavite, the
sloping agricultural land technology (SALT) designed and promoted by the Mindanao Baptist Rural
Life Center (MBRLC) in Davao del Sur, the vegetable-agroforestry (VAF) systems of the World
Agroforestry Center (ICRAF) in Bukidnon, and the complex upland food-production systems of
different indigenous peoples’ communities all over the country (Fernandez, R.A., 2003).
By copying the structure of the tropical rainforest, the farmers in Cavite have shown how
productivity could be maximized. Their multi-storey cropping system is a successful adaptation to the
tropical environment where maximum and efficient utilization of sunlight and space is practiced. The
forestlike farms of Cavite have several storeys of cultivated plants with coconut occupying the upper
layer. Beneath are medium-tall trees such as jackfruit (Artocarpus heterophyllus), mango (Mangifera
indica), avocado (Persea americana), santol (Sandoricum koetjape), lanzones (Lansium domesticum)
and guava (Psidium guajava). At the lower level, a canopy of leaves is formed by banana (Musa spp.),
coffee (Coffea robusta and C. arabica), and papaya (Carica papaya) which are the main cash crops.
The thinner trunks then support twining plants like black pepper (Piper nigrum), yam (Dioscorea alata),
passion fruit (Passiflora edulis), patola and squash. Below these high diversity of plants grow shadeloving crops such as taro (Colocasia esculenta), arrowroot (Maranta arundinacea), sweet potato
(Ipomoea batatas), and cassava (Manihot esculenta). These are randomly planted as good sources of
food and animal feed.
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Other root crops like ginger are also added as sources of cash. Pineapple (Ananas comosus) is
one of the main cash crops that occupy the lowest layer. It is usually planted when the coffee is still
establishing itself and is the main source of cash when coffee is not yet bearing fruits. Pineapple is
drought and typhoon tolerant and these effectively suppress weeds thus, reducing labor cost.
Multi-purpose trees like kakawate (Gliricidia sepium) and ipil-ipil (Leucaena leucocephala)
are planted on the border to serve as live fence. These are also mixed with fruit trees and provide
shade for the coffee and black pepper while the leaves are used as feed for livestock. Falling leaves
and pruning provide mulch and fertilizer for the soil.
The Cavite system (Zamora et al., 2015) is coconut-based with a complex combination of
annuals and perennial crops. Some successful combinations are:
i. Coconut (Cocos nucifera) + Papaya + Pineapple + Taro
ii. Coconut + Upland rice (Oryza sativa) + Pineapple + Daisy (Bellis perennis) +
Banana + Sweet potato + Sayote (Sechium edule ) + Ginger
iii. Coconut + Coffee + Upland rice + Corn + Papaya + Pineapple
iv. Coconut + Banana + Lanzones + Coffee + Taro
v. Coconut + Papaya + Banana + Kakawate + Black pepper + Taro + Pineapple
It should be noted, however, that these crop combinations may not work in other areas. This is
because, it appears that continuous selection for varieties adapted for localized farming conditions
have been going on for ages in these areas. Almost all the farmers do their own selection of materials
to plant, and many of them maintain a nursery where selected planting materials are propagated,
maintained and adapted to local conditions (Magat, S.S., & Secretaria, M.I.,,2005).
Another version of the coconut-based multi-storey cropping system is the 1:4 Pooc II
Agroforestry, where it stands for one hectare and 4 for the number of crops simultaneously grown.
The most common combination is coffee + black pepper + papaya + banana, lanzones and mahogany
(Swietenia macrophylla) and other variations.
In the multi-storey structure of planting, there is maximum utilization of sunlight. Soil
conservation is also improved. Strong sunlight is filtered by the leaves which prevent it from striking
the soil directly. The same is true with rainfall whose soil-beating effect is moderated by the leaves.
The litter minimizes soil erosion and increases the water holding capacity of the soil. In effect, there is
high organic matter build-up. Nature has shown that the tropical forest could be highly productive yet,
delicate and vulnerable. The muti-storey cropping system imitates the forest that once covered the
Cavite slopes, it is highly productive and yet, protective to its environment (Padilla, 1999).
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In summary, this indigenous agroforestry system of combining different crops in a multistorey structure results in (a) reduced risk that may be associated with natural calamities and climate
change, as harvest is spread over the year; (b) even distribution of labor and income rather than
seasonal as in the case of mono cropping;(c) less work as tillage is minimal and work is mainly
planting and harvesting; and (d) reduced pest infestation as a result of the high diversity of crops.
MAPPING THE INNOVATION SYSTEM OF CROP PROTECTION TECHNOLOGIES
Analysis of the innovation system of bio-fertilizers way. Innovation systems can be compared
to social could reveal factors that constrain the sustained adoption systems in a manner that the former
does not only focus of this innovation. An understanding of the role of the on the degree of
connectivity among the different actors innovation system domain actors and their but also on the
learning and adaptive processes that make interrelationships could help unravel the complex the
system active and evolutionary. It puts emphasis on interaction between the different factors that affect
bio- the role of farmers, input suppliers, transporters, fertilizer adoption. It could guide decisionmakers in processors and markets in the innovation process. In formulating appropriate actions to
ensure that farmers brief, it focuses on the generation, diffusion and reap the economic and
environmental benefits that can be application of knowledge.
Choice of crop protection technologies under risk: an expected utility maximization
framework. The uncertainty of pest attacks warrants the use of stochastic models in measuring the
impact of crop protection technologies on agricultural productivity and income. Many of the stochastic
elements, risks, in pest control stem from variations in agricultural biology, including variations in
pest numbers and types over time and space: crop susceptibility to pest attack across crops, varieties,
and crop growth stage; and pest susceptibilities to chemical, mechanical, and other controls.
Pesticide, labor, and other pest control inputs have an important effect on risk and uncertainty
in agricultural production. Since most uncertainty in pest control is due to uncertain pest infestation
levels, and chemical inputs act on these infestations, randomness enters the production function
through the productivity of the pesticides (Leach, A.W. & Mumford, J.D. (2011).
Taking production risk and producer risk attitudes into consideration, this chapter presents an
assessment of the various crop protection technologies, including complete control, economic
threshold (ET) levels, and natural control as well as farmers’ technologies.
An expected utility function is used to rank technologies where expected utility is based on
decisionmakers’ subjective probability distributions of the random variable in profit. Profit or net
benefit variability is directly related to yield variability, which is directly related to insect damage
variability, among other variables.
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The social costs of current crop protection technologies, once recognized, made the search for
sustainable pest management technologies imperative. In developed countries, the damage done by
conventional pest management technologies to the environment has triggered the development of
integrated pest management (IPM). In developing countries, the shift from polyculture to the more
modern monoculture has opened up the need for chemical control of pests, especially in the rice world.
Development of pesticide resistance and the increasing health risks to users may have created
initiatives for developing sustainable pest management technologies in developing countries. However,
for sustainable technology to be adopted, it will have to fit the management capabilities of farmers.
The institutional and economic structure in the rural sector of developing economies is such
that some policy intervention would be needed to reconcile long-term societal objectives and shortterm individual objectives in pest control. Farmers are focused on family survival and general wellbeing and may use practices and resources in a way that is unsustainable from society's perspective.
Government seeks self-sufficiency in food, but at a minimal social cost. Its role, therefore, is to
provide farmers with appropriate policy incentives to use sustainable practices.
The key issues for crop protection extension are quality control and accountabi1ity. Even the
latest locally validated research results remain mere academic or bureaucratic exercises if they are not
passed accurately to extension agents and on to farmers.
COMPOSTING
Growing concerns relating to land degradation, the inappropriate use of inorganic fertilizers,
atmospheric pollution, soil health, soil biodiversity and sanitation have rekindled global interest in
organic recycling practices such as composting. The potential of composting to turn on-farm waste
materials into a farm resource makes it an attractive proposition. Composting offers benefits ts such as
enhanced soil fertility and soil health that engender increased agricultural productivity, improved soil
biodiversity, reduced ecological risks and a better environment. However, many farmers, and
especially those in developing countries find themselves at a disadvantage as they fail to make the best
use of organic recycling opportunities. These farmers work under various constraints relating to: a lack
of knowledge on efficient
expeditious technology; long time spans; intense labour, land and
investment requirements; and economic factors.
As there is an extensive literature on composting methodology, this review presents only a
selective and brief account of the salient approaches. It makes a broad distinction between small-scale
and large-scale composting practices. While small-scale production systems normally employ
infrastructure and techniques that are technically and financially more feasible to farmers, large-scale
systems require investment for containers and/or turning, as well as greater knowledge and skills to
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control the process. Therefore, the former may serve individual small-scale composters as technology
packages that are financially NE-tuned to suit specific c circumstances, and the latter as a means to
meet quantum requirements of an individual or group of individuals.
The review also makes a distinction between traditional and rapid composting practices. The
distinction is based mainly on the difference between those practices adopted as a convention and
recent introductions for expediting the process that entail individual or combined application of
treatments such as shredding and frequent turning, mineral nitrogen compounds, effective
microorganisms, use of worms, cellulolytic organisms, forced aeration and mechanical turnings.
Traditional methods generally adopt an approach based on anaerobic decomposition or one
based on aerobic decomposition using passive aeration through measures such as little and infrequent
turnings or static aeration provisions such as perforated poles/pipes. These processes take several
months. On the other hand, using the recently developed techniques mentioned above, rapid methods
expedite the aerobic decomposition process and reduce the composting period to about four to
financially weeks. Most of these methods include a high temperature period and this adds further
value to the product by eliminating pathogens and weed seeds.
Traditional methods based on passive composting involve stacking the material in piles or pits
to decompose over a long period with little agitation and management. Using this approach, the Indian
Bangalore method permits anaerobic decomposition for a larger part of operations and requires six to
eight months to produce compost. The method is mainly used to treat urban wastes in the developing
world. A similar method employed on large farms in the Western Hemisphere is passive composting
of manure piles. The active composting period in this process may take one to two years.
The Indian Indore methods enhance passive aeration slightly through a few turnings, thereby
permitting aerobic decomposition and enabling production in a time span of about four months. The
Chinese rural composting pit method uses a passive aeration approach through turnings to provide
output in two to three months. The above methods are in widespread use in the developing world.
Although the labour requirements for these methods are high, they are not capital intensive and do not
require sophisticated infrastructure and machinery. Small farmers find them easy to practice,
especially where manual labour is not a constraint. However, the low turnover and longer time span
are the major drawbacks of these methods.
In addition, there is another recently introduced approach called vermicomposting.
Vermicomposting is not composting as such because it is not the decomposition of organic materials
by micro-organisms, but enzymatic degradation through the digestive system of earthworms. It is the
casts of the worms that are utilized. Vermicomposting results in high quality compost and does not
require physical turning of the material. In order to maintain aerobic conditions and limit the
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temperature rise, the bed or pile of materials needs to be of limited size. Temperatures need to be
regulated to favour the growth and activity of worms. However, it has a lower turnover than other
rapid methods and the composting process takes 6–12 weeks.
In some circumstances, a combination of aerobic decomposition, anaerobic decomposition and
vermicomposting may be useful for the more effective production of high-quality compost. Integrating
traditional composting and vermicomposting is one such example. In this approach, while the high
temperature ensures better quality through the destruction of pathogens and weed seeds, worms
perform the roles of turning and maintaining an aerobic condition, thereby reducing the need for
investment and labour (Garg P, Gupta A, & Satya S, 2006).
Composting may be divided into two categories by the nature of the decomposition process. In
anaerobic composting, decomposition occurs where oxygen (O) is absent or in limited supply. Under
this method, anaerobic micro-organisms dominate and develop intermediate compounds including
methane, organic acids, hydrogen sulphide and other substances. In the absence of O, these
compounds accumulate and are not metabolized further. Many of these compounds have strong odours
and some present phytotoxicity. As anaerobic composting is a low-temperature process, it leaves weed
seeds and pathogens intact. Moreover, the process usually takes longer than aerobic composting.
These drawbacks often offset the merits of this process, viz. Little work involved and fewer nutrients
lost during the process.
Aerobic composting takes place in the presence of ample O. In this process, aerobic
microorganisms break down organic matter and produce carbon dioxide (CO2), ammonia, water, heat
and humus, the relatively stable organic end product. Although aerobic composting may produce
intermediate compounds such as organic acids, aerobic micro-organisms decompose them further .
The resultant compost, with its relatively unstable form of organic matter, has little risk of
phytotoxicity. The heat generated accelerates the breakdown of proteins, fats and complex
carbohydrates such as cellulose and hemi-cellulose. Hence, the processing time is shorter. Moreover,
this process destroys many micro-organisms that are human or plant pathogens, as well as weed seeds,
provided it undergoes Sufficiently high temperature. Although more nutrients are lost from the
materials by aerobic composting, it is considered more efficient and useful than anaerobic composting
for agricultural production.
Bin composting is perhaps the simplest in-vessel method. The materials are contained by walls
and usually a roof. The bin may simply be wooden slatted walls (with or without a roof) a grain bin, or
a bulk storage building. The buildings or bins allow higher stacking of materials and better use of fl
floor space than free-standing piles. Bins can also eliminate weather problems, contain odours, and
provide better temperature control.
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Bin composting methods operate in a similar way to the aerated static pile method. They
include some means of forced aeration in the fl floor of the bin and little or no turning of the materials.
Occasional remixing of material in the bins can invigorate the process. Where several bins are used,
the composting materials can be moved periodically from one bin to the next in succession. Most of
the principles and guidelines suggested for the aerated pile also apply to bin composting. One
exception relates to relatively high bins. In this case, there is a greater degree of compaction and a
greater depth of materials for air to pass through. Both factors increase resistance to air flow ow
(pressure loss). A raw material with a stronger structure and/or a higher pressure blower may be
required, compared to the aerated static pile method.
VERMICOMPOSTING IN THE PHILIPPINES
Lumbricus rubellus and/or Perionyx excavator can be reared and multiplied from a
commercially-obtained breeder stock in shallow wooden boxes stored in a shed. The boxes were
approximately 45 cm × 60 cm × 20 cm and had drainage holes; they were stored on shelves in rows
and tiers. The bedding material comprised miscellaneous organic residues such as sawdust, cereal
straw, rice husks, bagasse and cardboard, and was well moistened with water. The wet mixture was
stored for about one month, being covered with a damp sack to minimize evaporation, and was mixed
thoroughly several times. When fermentation was complete, chicken manure and green matter, such as
ipil ipil leaves or water hyacinth, were added. The material was placed in the boxes. It was sufficiently
loose for the worms to burrow and it was able to retain moisture (Virginia, C.C. 1997).
The proportions of the different materials varied according to the nature of the material, but
the aim was to achieve a financially protein content of about 15 percent. A pH value as near neutral as
possible was necessary and the boxes were kept at temperatures between 20 and 27 °C (at higher
temperatures, the worms aestivate; at lower temperatures, they hibernate).
Although the worms were able to eat the bedding material, the worms were fed regularly at
this stage: every kilogram of worms received 1 kg of feed every 24 hours. For each 0.1 m2 of surface
area, 100 g of breeder worms were added to the boxes. The feed stuffs included chicken manure, ipil
ipil, and vegetable wastes. At one farm, water hyacinth was grown specific and used fresh (chopped
up) as the sole source of feed. Some form of protection was required against predators (birds, ants,
leeches, rats, frogs and centipedes).
A series of pits (the number depending on the space available) were dug approximately 3 m ×
4 m × 1 m deep, with sloping sides. Bamboo poles were laid in a parallel row on the pit floor and
covered with a lattice of wood strips. This provided the necessary drainage as the worms could not
have survived in a waterlogged environment.
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The pits were lined with old feedstuff sacks to prevent the worms from escaping into the
surrounding soil and yet permit drainage of excess water. The pits were then financially with rural
organic residues such as straw and other crop residues, animal manure, green weeds, and leaves. The
filled pits were covered loosely with soil and kept moist for a week or so. One or two spots on the
heap were then well watered and worms from the breeding boxes were place on top. The worms
burrowed down immediately into the damp soil.
In order to harvest the worms from the boxes, two-thirds of the box was emptied into a new
box lined with banana leaf or old newspaper. The original box was then provided with fresh bedding
material and those worms remaining multiplied again. The worms emptied from the box were picked
out by hand for adding to the heap.
The compost pits were left for a period of two months; ideally such pits should be shaded from
hot sunshine and kept moist. Within two months, about 10 kg of castings had been produced per
kilogram of worms. The pits were then excavated to an extent of about two-thirds to three quarters and
the bulk of the worms removed by hand or by sieving. This left
composting, and the pit was
worms in the pit for further
with fresh organic residues. The compost was sun-dried and sieved to
produce good quality material.
INTERCROPPING PRODUCTION
inter cropping vegetable under tree-based system is becoming popular practice in the uplands.
Little information is available on the potentials of different vegetables species under tree-based
systems. We hypothesised that in an intensive commercial vegetable production system in the uplands,
monoculture system is not sustainable but integrating trees is feasible and offers better prospects. Our
overall objective is to-integrate trees on intensive vegetable farming system with minimal negative
interaction, thus increasing productivity, profitability, nutrient use efficiency and environmental
services.
VEGETABLE AGROFORESTRY SYSTEM
Vegetable agroforestry system (VAFS) is a cultivation of vegetables together with trees
simultaneously which components are arranged spatially in order to achieve both the economic and
environmental benefits of the farming system. Trees and vegetables interact in VAF systems (Mercado,
AR et al. 2008).
Interaction is defined as the effect of one component of a system on the performance of
another component and/or the overall system. Plant interaction can either be competitive,
complementarity or supplementarity for growth resources, such as nutrient, water and light.
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Complementarity occurs when trees take up nutrients and water from soil profiles, which would not be
available to the associated crops, sparing water and nutrients for the shallow rooted annual crops. The
net complementarity effect depends on to what degree it is offset by competition, which exists when
trees and the associated vegetables share the same growth resources at the same soil layer, and they are
not enough for both crops’ basic physiological functioning. This competitive situation represents most
of the upland areas in the Philippines, and throughout the tropics of Southeast Asia where soils are
acidic and inherently poor in soil nutrients. At smallholder context, it is desirable to obtain the high
outputs from limited growth resources of diverse products spread throughout the year in order to meet
the basic household needs (Mercado, A.R., Jr., Duque-Piñon, C., Palada, M., & Reyes, M.R., 2012).
In the context of hedgerow inter cropping system, competition interaction includes radiation,
water and nutrients, micro-climate, pest and diseases that include interactions related to weeds, insects
and diseases and allelopathy. In sloping areas, tree-soil-crop interaction is altered by the dramatic soil
spatial changes that occur as terraces developed behind the vegetative barriers. Tillage contributes
about 70% of soil movement from upper to lower portion of the alley, and this changes the below
ground interaction between trees and crops.
In terms of crop yields the progressive decline in crop productivity, as rows approach the
hedgerows, is attributed to a combination of above ground and below ground competition. Light,
water and nutrients are important components for plant growth, thus competition exists. On flat lands
in the tropics, inter crops with dissimilar heights are ideally laid out in an east-west direction, which
maximize direct sunlight and reduces light competition. The same goes in unidirectional slopes facing
either north or south. However, if contour planting is practised in cone-shaped slopes
(multidirectional), the trees tend to severely shade the crops, thus above competition exists. The tree
roots tend to be asymmetrical on slopes.
While a number of studies have already been conducted on cereal based systems tree-crop
interactions. Different tree species and vegetable types or varieties differ in their capacity to
complement or compete from a given pattern of resource availability. There are several factors may
affect vegetable-tree interaction in agroforestry system such as tree functional characteristics, tree root
architecture, tree canopy type, tree seasonality, tree age, soil chemical and physical characteristics,
vegetable types, rainfall pattern, planting orientation, silvicultural and horticultural management of
trees and vegetables, respectively. Tree functional characteristics include N2-fixing capacity,
phosphatase activity, mycorrhizal association, and among others.
VAF system is an agroforestry system in which vegetables are grown on alleys formed by
hedgerows of forage legumes, grasses or trees, particularly fast growing tree species, or vegetables
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planted parallel or perpendicular to tree rows as boundary planting, or vegetable planted around trees
planted in parkland system. This system provides many advantages, which farmers may not have fully
realised yet. It maximize farm outputs and minimises management costs because timber establishment
and maintenance costs can be charged to the vegetable production (Garrity & Mercado, 1994). The
trees improve nutrient use efficiency by recovering nutrients leached in soil layer beyond the reach of
shallow rooted vegetables. Trees also prevent soil erosion by increasing water infiltration while
reducing lateral runoff thus minimizing downstream water quality problems. Such advantages are on
top of the environmental services provided by tree integration on farm such as increasing farming
systems capacity to carbon stock as well as enhancing agri-diversity.
Despite of the benefits of growing vegetable in association with trees, a greater number of
vegetable farmers are still practicing monoculture. With limited literatures available on VAF, there is a
need to provide technical information to farmers as a decision support strategy for tree-vegetable
matching, silvo-horticultural management, fertility and pest and diseases management. Understanding
the interactions of the different components in VAF systems and evaluating their potentials are equally
important for farmers to evaluate their management options – minimising competition and maximising
complementarity, thus increasing total system productivity, economic profitability, nutrient use
efficiency as well as environmental services of the vegetable farming systems.
Integration of indigenous tree vegetables into smallholders system is important to insure
sustainable supply of vegetables to the poor households in the rural communities which were generally
dependent on the seasonal supply of semi-temperate vegetables. Growing these tree vegetables at their
backyards will provide 365- day supply of nutritious vegetables thus ensuring food and nutritional
security of the households (Paragas, R.T., 2011).
The cited authors worked with tree vegetables such as Bago (Gnetum gnemon ), Malungay
(Moringa oliefera), Lagikway (Abelmuchos manihot), Katuray (Sesbania grandiflora), and Chinese
malungay (Sauropus androgynous) were raised in the nursery by using 20-cm cuttings treated with
Indole-3- butyric acid (IBA) at 1500 ppm concentration. Cuttings were planted in 2 x 5 inches plastic
bags. Cuttings were rooted in clonal propagation chamber, and were transferred later to a black plastic
net shed nursery for two months. Seedlings were hardened for another month before field planting.
The seedlings were laid out in 1.2 x 18 meters long plot perpendicular to the tree rows of Eucalyptus
torillana. Seedlings were planted in a single row at 50 cm apart. For basal, chicken dung was applied
at the rate of 100 g per plant. N was applied as side dressing at 30 and 60 DAP at the rate of 20g per
plant. No application of pesticides was done.
Water competition is a major issue in integrate type vegetable agroforestry system particularly
when trees and associated vegetables take up water on the same soil layer. This is exacerbated if
rainfall distribution is erratic under Rain field environments. This particular phenomenon leads to
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lower overall system productivity. Drip irrigation system will dramatically improve sustainable water
availability to intended vegetables as well as to the companion trees, thus eliminating water
competition.
The objectives of this study were to alleviate water competition between tree crop and
vegetable crop by providing sufficient supply of water to the associated vegetable crop through drip
irrigation method, thus enhancing net complementarity, and to determine the effect of drip irrigation
on the bell pepper production. The following treatments employed were:
1. With drip irrigation.
2. Without drip irrigation.
3. Tree root pruning.
Bell pepper seedlings were prepared as indicated above, and were transplanted in a double row
100 cm apart and 40 cm between plants perpendicular to the tree row of six years old Eucalyptus
torillana. Standard horticultural management of bell pepper was followed except for the application of
drip irrigation indicated as treatment and the tree root pruning. Root pruning was done by digging
1.5m deep, 0.25m wide and 1.5m long parallel to the tree line of Eucalypti torillana and between the
bell pepper plot. The digging was done 25 cm from the tree trunk. A plastic sheet of 0.03 mm
thickness was laid out 1.5m parallel to the tree line. The digging was filled up with soil after the
installation of plastic sheet.
Eighty percent of the VAF farmers interviewed indicated competition between trees and
vegetable crops, like yellowing of leaves adjacent to the trees (84%) or leaves are less green. They
recognized from low (33%), moderate (42%), and high competition (17%) between trees and
vegetable crops. The competition started during the early growth stage of vegetables up to harvesting.
Severe competition was observed from 2nd year and up to more than 5 years of tree age (80%).
Ninety percent of the farmers recognized shading (light competition) was the main problem,
thus 73% of VAF farmers pruned the trees before planting vegetables, and they did it every 1-2 years
interval (64%). Farmers removed about 50% of the canopy (18%), but most of them completely
removed all the leaves (55%). Farmers planted the vegetables 1-2 meters away from the trees (84%).
Thirty percent of the VAF farmers mentioned that they applied fertilizer to the trees. When they
applied fertilizers to the vegetables, some VAF farmers put more fertilizers to the vegetables grown
near the trees to alleviate competition (69%).
Most of VAF farmers indicated the litter falls (leaves, twigs and other debris during prunes)
created difficulty during land preparation (91%). They also indicated presence of roots in the fields
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(61%) which also contributed to difficulty during plowing. Most of the VAF farmers indicated
difficulty of land preparation when trees and vegetables are integrated (91%).
We have assessed existing VAF systems covering 21 farms, 5 tree species, 8 vegetables, 4
aspects. Data collected were tree parameters (stem diameter, tree height, canopy height and width),
spatial performance of vegetables (height, stem diameter, crown width, biomass), spatial light
transmission (fish eye photography/quantum light meter).
The growth and yield of vegetables were taken spatially from the tree line outward indicating
three zones of response curve: competition, complementarity and neutral zones. The competition zone
was the distance from the tree line outward where the yield was lower than the neutral zone. Under
farmers’ management, vegetables were planted 1-2 meters from the trees, thus this portion was part of
the competition zone, and pulling down the net complementarity effect as indicated in the equation
above. The competition zone extended up to about 6 meters from the tree line. The complementarity
zone is located where the performance of vegetable is greater than the neutral zone up to the location
where vegetable performance decline and level off equal to no tree influence, which is the neutral
zone. The complementarity zone usually lies between 6m to 15m away from the tree line. Plant height,
marketable yield and plant stem diameter were affected by this tree- vegetable interaction relative to
the tree distance. Thus in order to optimize the benefit of having trees on farm without compromising
the productivity of the associated annual crops, like vegetables, tree spacing must be done to optimize
the height and the width of the complementarity zone so that the value at the competition zone can be
offset. There were cases that increase of vegetable yields at the complementarity zone was not able to
compensate the reduction of yield at competition, particularly if farmers were not planting vegetables
two meters away from the tree line.
In improving the VAF total system productivity, these 3 zones should be looked at in depth
and find ways on how to reduce the width and height of the competition zone while increasing the
width and height of complementarity zone. The tree rows spacing should be 2 times the distance of the
peak of complementarity zone which is 10-12 meters from the tree line, thus the optimum tree spacing
should be at 20-25 meters apart. Tree-vegetable matching must be based on how the vegetables able to
adapt under tree based as well as how the vegetables able to increase the height and width of the curve
in complementarity zone.
Farmers generally pruned the trees about 40-50% of the canopy as normal agricultural
recommendation for forest trees. With this canopy removal, light transmission can be at 70% (Figure 2)
compared with open field. Vegetables, which are generally having C3 photosynthetic pathways, are
supposedly able to adapt this amount of light transmission. Some farmers do not prune the trees (10%
of the respondents), thus light transmission can be as low as 10-20% at 1-3 m from the tree line, light
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competition can be severe. Many farmers removed all the small branches, twigs and leaves, leaving
the trees like huge standing candle.
During the wet season planting (June – October 2007), there were 3 types of indigenous
vegetables planted such as leafy, fruit and climbing. Among the leafy vegetables, Amaranthus TOT
7278 from Bangladesh, Amaranthus TOT 4141 from Vietnam and Jute 3504 had the highest
marketable yields under Lantapan, Bukidnon condition, and had the highest yields in the
supplementarity zone as well as yield at competition zone. Although some leafy vegetables had low
marketable yields such as Alugbati’s, Roselle, some Jutes accessions, all responded positively with the
presence of trees, except for Amaranthus TOT 7278 and Saluyot TOT 4413. Saluyot TOT 6667 and
Amaranthus TOT 2272 from Taiwan responded strongly to tree hedgerows.
Among the fruit vegetables, eggplants yielded significantly higher than Okra. All eggplant
varieties evaluated yielded high, but SOO-632 yielded the highest. These eggplants also responded
well to the presence of tree with increase yield (PY) from 10-20%, and SOO-168 had the highest yield
increase (PY) of 20%. Although yield of Okra was low, but it has responded well to the tree hedge
thus having a high PY of 30%, which means that AF was able to increase yield of Okra by 30%.
INTEGRATION OF GREEN MANURES INTO THE CROP ROTATION
Green manures fall into two basic types when considering where to place them in the rotation.
Examples of the first type include grass/clover leys, lucerne and other long-term fertility builders that
are used to provide the fertility foundation for a period of cropping. The duration of the fertility crop
and the subsequent cropping will both depend on a number of factors. A key factor is the inherent
fertility of the soil – where this is good the cropping period can be maximised. Other factors include
the type of cropping – if this is a combination of field vegetables and cereals then the fertility crop can
be under sown into a cereal at the end of the cropping period.
This should ensure a more reliable establishment of the ley and avoids the need for autumn
cultivation. This can be a problem where the fertility crop is being established following a vegetable
crop. This crop must be cleared early to allow time for establishment of the ley otherwise a spring
sowing will be necessary. There is a growing interest in the idea of under sowing into vegetable crops
(e.g. red clover into sweetcorn) though more work is needed before reliable recommendations can be
made.
A different approach is needed for the short-term green manures as there are more factors to
be considered.These include previous and following cropping, establishment time, frost hardiness, and
soil type. The work described earlier on the release of nitrogen from incorporated green manures
means that the requirements of the following crop should be taken into account. As an example lettuce
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could follow vetch and leeks could follow rye to make the best use of released nutrients. Rye has been
shown to be the most effective overwinter nitrate scavenger and should be considered for use on
lighter soils that could be more prone to leaching. Allowance should also be made for the timing of
incorporation and breakdown; a minimum period of 2-4 weeks should be allowed to avoid the
possibility of allelopathic materials released during breakdown inhibiting germination of the following
crop. This can occur for all crops although vetch is said to have the strongest effect (Kamo et al, 2003).
These general principles are well established and a vast amount of research work has been
done to investigate specific effects of green manures. However, more work is needed on the practical
value of green manures in a wider range of situations.
BACKYARD AND COMMUNITY - GARDENING IN THE URBAN PHILIPPINES.
In 2003, the World Health Organization (WHO) and the Food and Agriculture Organization
(FAO) of the United Nations launched a joint initiative to address sharp rises in major noncommunicable diseases linked to low fruit and vegetable consumption. Such collaborative efforts
reflect growing macro level concerns about the premature mortalities and losses in global productivity
attributable to diets lacking in key micro nutrients, fibers, and various non-nutrient substances
associated with these kinds of agricultural commodities.
Indeed, both the long and near term outlook presented by the WHO/FAO on this matter
appears rather bleak. Thanks in part to the rising influence of Western eating habits and nutritional
regimes in diverse populations across Africa, Asia, Latin America, and elsewhere now increasingly
suffer the deleterious effects of chronic medical conditions such as cardiovascular disease,
gastrointestinal cancer, Type 2 diabetes, and obesity. This development, coupled with a concomitant
shift away from unvaried diets of traditional and mostly simple fare towards more diverse ones based
around unhealthy, animal-source, and processed foods containing high concentrations of sugar and fat,
emerges as a troubling symptom of accelerating global modernity.
As many low and moderate income nations across the Global South grapple with the
complexities and contradictions arising from an intensifying nutrition transition (Popkin & GordernLarsen, 2004), government policymakers and health care professionals look for new and innovative
ways to negotiate the rapidly changing public health landscape. Doubtless, these tasks are complicated
by the fact that until recently the health care apparatus of most less-developed countries were oriented
primarily towards problems of hunger and under nutrition. Implementing approaches that continue to
address these long-standing medical conditions while simultaneously meeting the challenges arising
from the encroachment of various non-infectious diseases heretofore mainly associated with the
Global North seems nothing if not a highly ambitious undertaking. Such efforts emerge as all the more
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formidable given the extensive undercapitalisation and fragmentation that besets most health care
systems throughout what was once called the Third World.
Clearly, the chronic disease burden propagated by this dietary deficiency could be
significantly mitigated among affected populations if local consumption patterns better adhered to the
WHO’s recommended minimum daily intake of 400g or five equivalent 80g servings of fruits and
vegetables per individual. Just how realistic these guidelines are for those living in today’s Global
South appears rather questionable amid the increased economic volatility and soaring food costs4 that
have rocked global markets over recent years.
Thanks largely to processes of neoliberalism and economic globalisation, food access for
millions of those living in less-developed countries is now increasingly contingent upon a reliable cash
income. Within this context, the prospects of many households to meet basic food needs are
effectively undermined as under/unemployment remains so pervasive across the Global South.
Compounding the situation is the continued demise of traditional subsistence farming as more and
more tracts of arable land are subject to advancing corporate agricultural interests. In a very real sense,
Big Agribusiness’ hegemony over contemporary eating habits, food pricing, and cultivation practices
has significantly altered access to fruits, vegetables, and other everyday commodities for many
households in the Global South.
The sheer scope and complexity of this burgeoning health crisis belies the fact that inadequate
fruit and vegetable intake is not something fundamentally intrinsic to the Global South Left unchecked,
the overall impact of this dietary failure stands to exacerbate pre-existing health disparities both within
less-developed countries and between poorer nations and their more affluent counterparts. Such
prospects bode well for neither future economic development nor political stability within the affected
societies.
Organic and recycled materials play a central role in local backyard and community gardening,
as the example of barangay Anonas makes clear. Practices that promote conservation such as
refashioning plastic receptacles and other everyday items into growing pots (e.g. “container
gardening”) not only minimise municipal waste, they also reduce the harmful gases and smoke
associated with burning household trash, a common practice in today’s Philippine neighborhoods.
Moreover, the potentially adverse effects of gardening with chemical fertilizers and pesticides are
largely avoided through a reliance on organic products. Incorporating non-synthetic inputs into local
gardening practices serves as a sustainable and cost-effective option for barangay residents, as the
conventional farming methods of more highly capitalised ventures involve significant financial outlays
and risk groundwater contamination through the gradual buildup of nitrogen in the soil.
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CROP INTENSIFICATION VS. MORE DIVERSE PRODUCTION SYSTEMS
The required growth of agricultural production could be achieved by following the current
trend of greater agricultural intensification and yield improvements in developed countries and
additional land clearing in poorer countries with lower agricultural output per unit area. This would
lead to an increase of global land clearing of natural ecosystems to a total of about one billion ha by
2050, global agricultural greenhouse gas emissions to approximately 3 Gt per year of CO2-carbon
equivalents, and global N use to about 250 Mt per year. The production gains would come at the
expense of dramatic global environmental impact through a 2.4–2.7-fold increase in nitrogen- and
phosphorous-driven eutrophication of terrestrial, freshwater and near-shore marine ecosystems and
comparable increases in pesticide use. Eutrophication and habitat destruction would lead to massive
loss of biodiversity and ecosystem services and, consequently, loss of quality of life for mankind.
An alternative approach would be a moderate, sustainable intensification in existing croplands,
especially in regions or countries with relatively low yields, and by closing the yield gap between
potential and actual farm yield. This can be achieved through the development of new technological
improvements such as precision agriculture to optimize the use of inputs and the adaptation and
transfer of existing high-yielding technologies to low-yielding croplands.
Only three crops—wheat, rice and maize—covered 555 million ha or 40% of all arable land
globally in 2011 delivering more than 50% of human calorie intake. The 10 largest international seed
companies, which control two-thirds of the global seed market, focus exclusively on major staple
crops to ensure high returns on investments. The lower license fees paid to the self-pollinating wheat
crop makes this crop less attractive for breeders and may lead to a further concentration on only two
out of the three dominating crops.
Reliance on a handful of major crops has inherent agronomic, ecological, nutritional and
economic risks and is probably unsustainable in the long run, especially in view of global climate
change. It is now generally accepted that climate change will have a major impact on both biotic and
abiotic stresses in agricultural production systems and threaten yield and crop sustainability. Greater
diversity, which builds spatial and temporal heterogeneity into the cropping system, will enhance
resilience to abiotic and biotic stresses. There are many examples of successful pest and disease
suppression and buffering against climate variability in more diverse agroecosystems. Diversified
agroecosystems can be achieved in various ways: (a) through intraspecific genetic diversity in
monoculture systems (of rice, for example); (b) increased structural diversity in monocultures by
diversifying the plant age structure or strip-cutting fields so that natural enemies have a temporal and
spatial refuge; (c) diversifying crop land by growing grass strips or vegetation banks between and
alongside monocultures as a refuge for natural enemies; (d) temporal diversity can be achieved by
rotating cereal crops with broad leaf and nitrogen-fixing crops; (e) crop diversification by growing
compatible crop mixtures—two or more crop species—in the same field is reported to lead to disease
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suppression, climate change buffering and increased production; (f) growing crops and trees together
in agroforestry systems provides spatial and temporal diversity; (g) development of larger-scale
diversified landscapes at the farm or landscape level by integrating farmland with agroforestry,
livestock and silviculture (Andreas W. & Ebert, 2013)
Approximately 70% of the area in this region is used for irrigated cotton and winter wheat
under a state procurement mandate. The diversification into other crops like sorghum (Sorghum
bicolor), potato (Solanum tuberosum), indigo (Indigofera tinctoria), mungbean (Vigna radiata), and
maize (Zea mays) could lead to sustainable agriculture in the irrigated areas of Central Asia by
enhancing economic, ecological, and social conditions. Cropping system experiments conducted in the
US Corn Belt revealed that the diversification of the dominant corn-soybean cropping pattern with
small grains and forage legumes can result in a significant decrease in the use of agrochemicals and
fossil hydrocarbons without having a negative impact on yield and profitability. Other environmental
benefits such as improved soil and water conservation, better nutrient retention, and higher
populations of native plants and birds can be obtained by converting small amounts of crop land to
natural mixed grassland buffer strips. Furthermore, the integration of native perennial plant species
such as trees, different grasses and mixtures of multiple grassland species into the agroecosystem has
two major benefits: it can generate large amounts of bio fuel feed stocks and at the same time increase
soil carbon storage and decrease nitrogen emissions into drainage water.
Perennial species are sources of lignocellulose in contrast to the starch substrates derived from
conventional corn production for bio fuel purposes. Biodiverse agroecosystems are therefore seen as a
viable strategy to increase agroecosystem health and enhance resilience in the US Corn Belt.
In contrast to the above-mentioned major staple crops, underutilized, undervalued or neglected
crops—also branded development opportunity crops (DOCs) —are categorized in this article as
―minor cropsǁ that are already cultivated, but are underutilized regionally or globally given their still
relatively low global production and market value. Some of these crop species may be widely
distributed globally, but are restricted to a more local production and consumption system. Many of
these traditional crops grown for food, fiber, fodder, oil and as sources of traditional medicine play a
major role in the subsistence of local communities and frequently are of special social, cultural and
medicinal value. With good adaptation to often marginal lands, they constitute an important part of the
local diet of communities providing valuable nutritional components, which are often lacking in staple
crops.
As a result of the Green Revolution, many of those local, traditional crop species and varieties
have been replaced by high-yielding staple crop cultivars developed by modern breeding programs.
Traditional crops typically do not meet modern standards for uniformity and other characteristics as
they have been neglected by breeders from the private and public sectors. Thus they tend to be less
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competitive in the marketplace compared with commercial cultivars. Land races and crop wild
relatives have hitherto been increasingly valued and exploited for genes that provide increased biotic
resistance, tolerance to abiotic stress, yield and quality. However, use of agricultural biodiversity
should not be restricted to exploiting valuable genes for use in breeding programs if our aim is to
create more robust and resilient production systems. Currently underutilized food sources ranging
from minor grains and pulses, root and tuber crops and fruits and vegetables to non-timber forest
products have the potential to make a substantial contribution to food and nutrition security, to protect
against internal and external market disruptions and climate uncertainties, and lead to better ecosystem
functions and services, thus enhancing sustainability. A wider use of neglected and undervalued crops
and species, either inter cropped with main staples in cereal-based systems or as stand-alone crops,
would provide multiple options to build temporal and spatial heterogeneity into uniform cropping
systems, thus enhancing resilience to biotic and abiotic stress factors and ultimately leading to a more
sustainable supply of diverse and nutritious food.
Many traditional or indigenous vegetables are characterized by a high nutritional value
compared with global vegetables like tomato and cabbage. As source of essential vitamins, micro
nutrients, protein and other phytonutrients, traditional vegetables and underutilized legume crops such
as mungbean have the potential to play a major role in strategies to attain nutritional security.
Experiments with home gardens in India including about two dozen vegetable species have shown that
a small area of 6 m × 6 m can provide much of the vitamin A and C requirement for a family of four
during the entire year. Apart from the provision of essential vitamins, many of the vegetable crops
included in home garden kits are known to be naturally nutrient-dense. Community-based seed
conservation and multiplication has been used in the Philippines as an approach to enhance the
adoption of nutrient-dense traditional vegetables and to generate additional farm income.
Apart from their commercial, medicinal and cultural value, traditional vegetables are also
considered important for sustainable food production as they reduce the impact of production systems
on the environment. Many of these crops are hardy, adapted to specific marginal soil and climatic
conditions, and can be grown with minimal external inputs. This is the case, for example, in the
southern part of Rajasthan, India where due to the harsh climatic conditions only robust, droughttolerant traditional vegetables with short growth cycles such as Cucumis melo var. agrestis (kachri)
can survive and produce food.
Vegetables in general, but also many traditional vegetables such as amaranth (Amaranthus
spp.), jute mallow (Corchorus olitorius), African nightshade (Solanum scabrum), Asian (Solanum
melongena) and African (Solanum aethiopicum) eggplant, drumstick tree (Moringa oleifera), bitter
gourd (Momordica charantia), water spinach (Ipomoea aquatica), Chinese kale (Brassica oleracea var.
alboglabra), edible rape (Brassica napus), roselle (Hibiscus sabdariffa), Malabar spinach (Basella alba),
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slippery cabbage (Abelmoschus manihot), winged bean (Psophocarpus tetragonolobus) and many
gourd species are of considerable commercial value and thus can make a significant contribution to
household income. Hughes and Ebert cite a number of examples of profitable cultivation of traditional
vegetables in East and West Africa such as worowo (Solanacio biafrae), cockscomb (Celosia argentea),
African eggplant (Solanum macrocarpon), and amaranth.
Value addition by applying appropriate production and post harvest techniques ensures that
high quality produce reaches the market and satisfies consumer expectations. Consumer studies with
regard to the purchase and consumption of kale (B. oleracea) in Nairobi, Kenya revealed that urban
kale consumers care most for nutritional, sensory and safety attributes of the produce. The highest
estimates of willingness to pay more for the safety attribute of leafy vegetables were found in high-end
specialty stores (68%), followed by open-air markets (39%), supermarkets (34%), and roadside
markets (28%).
In Eastern Africa and Southeast Asia selected traditional vegetables are becoming an
increasingly attractive food group for the wealthier segments of the population and are slowly moving
out of the underutilized category into the commercial mainstream. Attracted by the strong market
demand, seed companies are beginning to explore and develop these popular crops, thus strengthening
the formal seed sector.
Not all traditional and underutilized crops can simply and easily be turned into commercial
success stories. Significant research, breeding and development efforts are needed to convert existing
local Land races of carefully selected, promising crops into varieties with wide adaptation and
commercial potential. An overview of breeding efforts and application of biotechnology tools such as
micro propagation, molecular marker studies and genetic transformation for the improvement of
underutilized crops has recently been provided by Ochatt and Jain and Jain and Gupta. Access to
genetic diversity of selected crops, either in situ or ex situ, is a pre-condition for success. Two
underutilized traditional vegetable crops—amaranth and drumstick tree—and the underutilized legume
crop mungbean are highlighted and briefly described. As indicated in section four, the term
―underutilizedǁ used here refers to as yet low global production and market value. All three crops
have the potential to assume a more important role globally in the sustainable supply of diverse and
nutritious food if given appropriate attention by plant breeders. The highlighted crops are well
represented in AVRDC’s genebank with substantial inter- and intra-specific genetic diversity, and all
three crops already have demonstrated their potential for wider adoption and commercial exploitation.
Amaranth (Amaranthus spp.) is widely grown as a leafy vegetable and for grain production
in many tropical countries in Africa, Central and South America, Mexico and parts of Asia. The genus
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Amaranthus consists of about 60 species, some of which have been cultivated for more than 5000
years. The main grain species are A. hypochondriachus (Prince’s feather), A. cruentus (purple
amaranth), and A. caudatus (Inca wheat), all of which have their center of origin in Mesoamerica and
South America. The following species are well-known as leafy vegetables: A. blitum (livid or slender
amaranth; origin: Mediterranean region in Central Europe), A. dubius, (spleen amaranth; origin:
tropical America), and A. tricolor; origin: tropical Asia). Although originally known as cereal
amaranth, A. cruentus is now the main vegetable amaranth in Africa, and to a lesser extent is also
found in Asia (Ebert AW, 2014).
Amaranth is ready for harvesting between 20 to 45 days after transplanting or sowing,
depending on the variety and harvest season. While low yields of leafy vegetables of less than 1.2 t/ha
are common in Africa, leafy amaranth has a yield potential of 32–40 t/ha and, therefore, is highly
competitive. Heavy rainfall in connection with typhoons often inflicts severe damage to leafy
vegetables grown in typhoon-prone countries in East and Southeast Asia. To avoid or reduce such
damage, production is moving into plastic houses in Taiwan during the summer months with
temperatures inside often reaching up to 40 °C. Amaranth, cucurbits, and water spinach (Ipomoea
aquatica) are some of the few crop choices under such extreme conditions. Water spinach proved to be
heat tolerant and amaranth moderately heat tolerant, while the majority of vegetable crops were either
heat sensitive or only slightly heat tolerant as indicated by the membrane stability of vegetable leaves.
As a C4-cycle plant, amaranth can sustain high photosynthetic activity and water use efficiency under
high temperatures and high radiation intensity, making it an ideal crop for abiotic stress conditions
under changing climates.
Amaranth is a very nutritious leafy vegetable, both in raw and cooked form. The nutritional
value of this crop is comparable to spinach, but much higher than cabbage and Chinese cabbage.
Amaranth is increasingly gaining importance both for household consumption and commercial
production in Africa and Asia. There is a good market potential for this crop, both in the high-price
and low-price segments. A small plot of amaranth of only 500 m2 can earn a farmer in Tanzania a
supplementary income of US$250 a year. Amaranth has made its way from Tanzania into
supermarkets in neighboring Nairobi, Kenya and the hotel catering business. Amaranth is often
produced with relatively low inputs and thus has low capital risk for small-scale farmers. Commercial
seed companies have recognized this market potential and are now including amaranth in their product
portfolio. Given the inter- and intra-specific diversity of cultivated amaranth, this crop is an ideal
choice for crop diversification, sustainable food production and nutrition security.
The Moringaceae family comprises 13 species that fit into three broad life forms with distinct
geographic origins. Four species belong to the group of bottle trees with bloated water-storing trunks:
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Moringa drouhardii (Madagascar), M. hildebrandtii (Madagascar), M. ovalifolia (Namibia and
southwest Angola), and M. stenopetala (Kenya and Ethiopia). Another three Moringa species are
characterized by slender trees with a tuberous juvenile stage: M. concanensis (India), M. oleifera
(India), and M. peregrina (Red Sea, Arabia, Horn of Africa). The remaining six tuberous Moringa
species are found in northeast Africa: M. arborea (northeast Kenya), M. borziana (Kenya and Somalia),
M. longituba (Kenya, Ethiopia, Somalia), M. pygmaea (northern Somalia), M. rivae (Kenya and
Ethiopia), and M. ruspoliana (Kenya, Ethiopia, Somalia).
M. oleifera is the predominant cultivated species of the Moringaceae family. It is widely
grown in the tropics of Asia, Latin America, the Caribbean and sub-Saharan Africa, and can also be
found in Florida and the Pacific Islands. It is a perennial softwood tree native to the sub-Himalayan
ranges of India, Pakistan, Bangladesh and Afghanistan. Moringa has already reached the status of an
economically important crop in India, the Philippines, Ethiopia, and Sudan (Ebert AW, 2014)..
Most parts of the tree are edible. The leaves and flowers are eaten as salad, as cooked
vegetables, or added to soups and sauces or used to make tea. The young, tender pods—known as
drumsticks—are highly valued as a vegetable in Asia and also are pickled. Fried seeds taste like
groundnuts. The root bark has a pungent taste similar to horseradish (Armoracia rusticana) and is used
as a condiment. Dried leaf powder is a good option to supplement diets of children and pregnant and
lactating women. For example, moringa leaf powder is added to a soybean and groundnut/peanut paste
to form an energy-dense supplemental food known as ready-to-use food (RUF) for treatment of severe
acute malnutrition.
Moringa has a high nutrient density and is rich in many essential micro nutrients and vitamins
as well as antioxidants and bioavailable iron. It excelled among 120 species of Asian traditional
vegetables tested for their content of micro nutrients and phytochemicals, antioxidant activity (AOA),
and traditional knowledge of their medicinal uses. Moreover, it is easy to grow, has excellent
processing properties, and good palatability. Drying moringa leaves in a low temperature oven at 50
°C for 16 hours maintained most nutrients and phytochemicals, except vitamin C. Boiling fresh
moringa leaves and dried powder in water enhanced aqueous AOA and increased bioavailable iron by
3.5 and 3 times, respectively (Bosch, C.H., 2015).
The Moringa family is rich in glucosinolates and isothiocyanates. Isothiocyanates are highly
reactive compounds that inhibit mitosis and stimulate apoptosis, a physiological process eliminating
DNA-damaged, unwanted cells in human tumor cells, and are therefore important to human health. A
recent analysis of the glucosinolate content of four moringa species maintained in the AVRDC field
genebank revealed that M. oleifera had a 3-fold higher glucosinolate concentration than M. stenopetala,
ranking second among the four species tested.
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Dietary or topical administration of moringa in the form of extracts, decoctions, creams, oils,
powders, and porridges have been reported in the scientific literature as having antibiotic,
antitrypanosomal, hypotensive, antispasmodic, antiulcer, anti-inflammatory, hypo-cholesterolemic,
and hypoglycemic activities. Moringa powder has been recommended as an immune stimulant in
HIV/AIDS treatment. In folk medicine, moringa flowers, leaves, and roots are used for the treatment
of various tumors, and seeds are specifically used to treat abdominal tumors. A dramatic reduction in
skin papillomas was observed following ingestion of moringa seedpod extracts.
Agronomic and horticultural uses. Moringa can be planted as a windbreak or living fence. It
has potential in alley cropping and as a component of agroforestry systems for sustainable vegetable
production. In some parts of Southeast Asia the tree is used as a support for climbers such as yams
(Dioscorea spp.), beans (Phaseolus spp.), and black pepper (Piper nigrum). Moringa can be inter
cropped with a range of vegetables such as cluster bean (Cyamopsis tetragonoloba), hot pepper
(Capsicum spp.), cowpea (Vigna unguiculata), and onion (Allium cepa). The leaves and twigs also
serve as forage for livestock. Moringa is grown as an ornamental tree in Latin America, the United
States, and Africa.
Moringa seed contains about 40% oil, known as ben oil. The oil is non-drying, resists rancidity,
and is used for cooking, lubrication, and in the cosmetic industry. The leftover pressed cake or ground
moringa seeds are used to purify drinking water and to flocculate contaminants. The wood can be used
for dying (blue color). The coarse fiber of the trunk is suitable for making mats, cordage, and paper.
Among 75 traditional plant-derived oils tested in India for bio fuel production, the oil derived
from M. oleifera showed good potential. The aptness of moringa oil for bio fuel production was
confirmed in a specific study using M. oleifera seeds from Pakistan. Biodiesel obtained from moringa
oil is characterized by a high cetane number of 67, one of the highest among biodiesel fuels.
Moringa is a fast-growing tree that adapts well to hot, semi-arid regions with as little as 500
mm annual rainfall. It also tolerates occasional wet or waterlogged conditions for a short period of
time, but prolonged flooding leads to a significant loss of plants. In general, moringa grows best in
lowland cultivation, but it also adapts to altitudes above 2000 m.
Greater use of moringa has good potential in the fight against hunger and malnutrition in the
developing world by improving nutrition and health of the rural and urban poor, increasing incomes of
smallholder farmers, and enhancing environmental services by controlling soil and wind erosion, and
providing shade and clean water. Given its multiple uses and wide range of adaptability, moringa is an
ideal crop for sustainable food production that would thrive as the climate changes. The highest global
production and consumption of pulses consisting mainly of chickpea, pigeonpea and mungbean is
found in South and Southeast Asia.
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Mungbean, Vigna radiata var. radiata, is a important legume crop in South and Southeast Asia,
but is also known and grown in Africa and the Americas on a still relatively small scale. The annual
mungbean production currently reaches more than six million hectares worldwide. This is already a
significant level of production for an underutilized crop, however, insignificant when compared with
the area covered by the major cereal crops. Half of the worldwide mungbean production is generated
in India (3 million hectares), followed by China and Myanmar. Mungbean is a good source of dietary
protein with high contents of folate and iron compared with many other legume crops. As it is a short
duration legume, it fits well into the fallow period between rice-rice, rice-wheat, rice-potato-wheat,
maize-wheat, cotton, and other cash crop cropping systems in use across the Indo-Gangetic plain.
Planting mungbean improves soil properties and provides additional nitrogen to subsequent crops. The
yield of rice following a mungbean intercrop can increase by up to 8% through the nitrogen fixed by
mungbean in the soil and due to reduced pest and disease pressure (Ebert AW, 2014)
The genus Vigna subgenus Ceratotropis consists of 17 recognized species that are naturally
distributed across Asia and are, therefore, also referred to as Asian Vigna. Among those 17 species,
eight species are considered as cultivated or semi-domesticated. In the 1980s the International Board
for Plant Genetic Resources (IBPGR) designated AVRDC as the international research and
development center with responsibility for the maintenance of the global base collection of mungbean.
The AVRDC collection currently consists of 6737 well-characterized accessions. The AVGRIS
characterization database contains detailed descriptions of 9198 accessions and sub-accessions, an
indication that in this crop many sub-accessions have been created due to clear variations of mainly
seed characteristics in the original accessions.
The majority of the mungbean accessions have been evaluated for morphological and
agronomic characteristics, nutritional composition, and resistance or tolerance to major pests and
diseases under replicated yield trials. Significant genetic divergence was found when comparing
AVRDC mungbean lines with varieties grown in India, offering a sound basis for further varietal
improvement.
Thirty years ago, mungbean was still a semi-domesticated crop cultivated on marginal land
with minimal external inputs. Early cultivars were indeterminate requiring multiple harvest cycles and
reached maturity in 90–110 days. They were highly susceptible to diseases and insect pests, had
problems with pod shattering, and yielded only about 400 kg/ha of small seed. AVRDC played a
significant role in the full domestication of the crop and in the development of short-duration
mungbean lines in Asia with a maturity period of 55–65 days, thus easily fitting into cereal-dominated
cropping systems. Major breeding objectives of the early mungbean improvement program at AVRDC
were lines with stable, high yield, determinate growth habit, early and uniform maturity, bold seeds,
less sensitivity to photo period and temperature and resistance to diseases and insect pests. Germplasm
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sources from the Philippines and India were instrumental in the development of improved varieties for
Southeast Asia. The gene pool from India contributed resistance to Cercospora leaf spot and powdery
mildew while the accessions from the Philippines provided traits for high yield, uniform maturity,
earliness and bold seed.
Further improvement was done by incorporating resistance to Mungbean yellow mosaic virus
(MYMV) from resistant lines developed in Pakistan. New improved mungbean varieties with
resistance or tolerance to MYMV, early and uniform maturity, and large-size seed have been
subsequently released to farmers in South Asia. The introduction of these new lines to National
Agricultural Research and Extension Systems (NARES) was achieved through the AVRDC
International Mungbean Nursery, which supplied promising lines annually for local screening and
evaluation. The yield potential of AVRDC-derived mungbean cultivars has doubled, pod maturity at
first harvest has increased to 80%, plants are less sensitive to photo period, and resistance to pests and
diseases has increased. These agronomic qualities favored the wide adoption of the new cultivars.
Recent variety releases in South Asia are listed in a publication by Chadha.
Mungbean production in Asia increased by 35% from 2.3 million t in 1985 to 3.1 million t in
2000 due to the introduction of improved AVRDC-derived lines. Close to 1.5 million farmers in Asia
adopted improved mungbean varieties on 50 to 95% of total mungbean area between 1984 and 2006,
realizing a yield increase of 28%–55%. During the same period consumption of mungbean increased
22%–66%, benefiting 1.5 million anemic children and leading to an estimated economic benefit due to
the improved health of anemic women of US$3.5 million to US$4 million per country.
With an average yield of about 400 kg/ha, the productivity of mungbean is still relatively low,
although it is similar to other pulse crops. Broadening the genetic base by selecting parents from
diverse cultivated and inter specific backgrounds is of great importance to achieve productivity gains.
Other major breeding goals are resistance to mungbean yellow mosaic disease and bruchid as well as
improvement of protein quality by selecting high methionine lines. AVRDC’s diverse mungbean
collection is the ideal storehouse for selection of accessions which might help achieve these new major
breeding goals. Draft whole genome sequences for mungbean and some wild relatives will become
available at AVRDC at the beginning of 2014, and this will strengthen genomics research and enhance
molecular and conventional breeding of this crop. Realizing the narrow genetic base of current
commercial mungbean cultivars in Australia, the Australian mungbean program has recently begun
evaluating and screening hundreds of AVRDC accessions for inclusion in their future national
breeding program. Once low yield and disease and insect pest problems of mungbean have been
successfully addressed by plant breeders, there is great potential for this crop to play a more
significant global role as an important source of vegetable protein.
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The intensive regional collaboration between AVRDC and national partners in recent years
has already led to the release of 125 improved mungbean varieties based on AVRDC breeding lines
and gene bank accessions in 29 countries worldwide from 1978 to 2013. The top ten countries that
released the highest number of lines from AVRDC-developed mungbean materials were China (21);
Vietnam (12); Bangladesh (8); Thailand (8), Australia (7); Korea (7); India (6); Indonesia (6);
Philippines (6); and Pakistan (6). Worldwide, improved AVRDC-derived mungbean lines constitute
now more than 25% of mungbean production.
As can be concluded from the examples of the three minor crops described in this article, and
in particular from the mungbean example, there is great potential for a number of currently
underutilized crops to play a major role in a more diversified and sustainable food production system.
However, there must be greater investment in long-term research and breeding programs and
improved seed supply sources for these crops to ensure they can be competitive in the marketplace.
Research and breeding of underutilized fruit and vegetable crops are clearly underfunded compared
with the few main staple crops. Substantial initial funding by the international donor community and
national state programs is necessary to achieve this goal and to generate interest among private sector
breeders once significant market potential is within reach.
RESTORATIVE EFFECTS OF LEGUMES ON AGRICULTURAL SOIL
These are documented in Greek and Roman literature, and have been exploited by farmers
since antiquity. However, the swellings or nodules on the roots were not linked with those benefits but
thought to be storage organs or of pathological origin, until the pioneering research of Drs. Hellreigel
and Wilfarth in Germany a little over a century ago. Hellreigel and Wilfarth's experiments compared
oat, buckwheat and rape, with pea, serradella and lupin, grown in sand culture with N-free nutrient
solution. A water extract of soil, containing an insignificant amount of N, was added to each pot. The
non-legumes remained N-deficient, whereas the legumes after a time recovered from "N-hunger"
became dark green and grew luxuriantly. It was concluded that the Papilionaceae obtained the N from
the atmosphere with the assistance of bacteria, from the soil extract, in the root nodules. Within a few
months of publication of these results, the great Russian microbiologist Beijerinck isolated nodule
bacteria, which he designated Bacillus radicicola, applied them back to legumes and satisfied Koch's
postulates. A new arena of scientific endeavour was born (FAO, 1998).
Bacillus radicicola has been replaced by several genera and many species of soil-borne
bacteria, the rhizobia, that infect, with varying degrees of specificity, certain groups of legume species.
The rhizobia proliferate in the rhizosphere of the potential host plant then penetrate the root epidermis,
either directly or via root hairs, and invade cortical cells. Host-cell division takes place, and highly
differentiated nodules develop within which atmospheric N2 is converted to ammonia by the
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microsymbiont and released to the host legume. Thus, an effectively nodulated legume can thrive in a
soil that is deficient in mineral N.
Prior to the mid-1970s, research interest in N2 fixation was restricted to a few groups of
scientists in Europe, USA and Australia. The energy crisis of 1973-1974 caused sudden, rapid
increases in the costs of nitrogenous fertilizers and stimulated interest hi legume N2 fixation and the
possibility of replacing chemical fertilizers with organic alternatives. Many developing countries were
particularly adversely affected by the increased costs of crop production, which stimulated research on
tropical legumes and their role in tropical agriculture.
Concomitant with this new interest in the biological fixation of atmospheric N2 in the 1970s
and the possibility of its exploitation for improved agricultural production in the developing world, the
isotope-dilution methodology was developed at the Agency, as a way of precisely measuring fixation
by field-grown legumes. A small quantity of !5N-enriched fertilizer is applied to the soil and the
legume assimilates atmospheric N2 supplied by the root-nodule symbiosis, in addition to the isotopeenriched N from the soil. Since non-fixing plants do not have access directly to atmospheric N2, the
resulting I5N/14N ratio of tissue in any two species differs in proportion with the amount of N fixed.
The isotope-dilution technique has been used extensively over the past 20 years in coordinated
research projects sponsored by the IAEA. A limitation of the isotope-dilution methodology is
uncertainty hi the choice of suitable non- N2-fixing reference species. The I5N/14N absorbed by the
fixing plant changes significantly with time, therefore, for a non-fixing species to be a suitable
reference, it must absorb 15N/14N with the same temporal pattern, and both should obtain their
mineral N from similar soil-N pools.
Occasionally, estimates of the amount of N fixed are negative as a result of the non-fixing
check having a different pattern of usage of the 14N and 15N pools; on the other hand, cereal species
have been shown to be acceptable non-fixing checks for some legumes. Of course where data appear
to be meaningful, they may not be so; it is advisable to use more than one non-fixing species to
provide comparisons of determinations of fixed N.
Although the energy crisis is long past, food security is increasingly under threat in many
developing countries of the tropics in which traditional agricultural systems are becoming
unsustainable as a result of demographic pressures. The global population is expected to double by
2040, and much of that increase will occur in developing countries in which hunger is already a threat.
Local needs to make arable land satisfy present food demands are resulting in overexploitation that results in ever-less productivity per unit area. When soil goes into a phase of rapid
decline in fertility, erosion often increases with far-reaching deleterious environmental consequences
that may be impossible to reverse. In such circumstances, crop productivity may not be significantly
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improved by even heavy applications of synthetic fertilizers, in the rare situation where such are
available to the subsistence farmer, because levels of organic matter that define fertility have reached
critically low values.
The pasture legumes have a dual role, sustaining animal production and supplying N to the
soil for use by subsequent cereal crops. Prior to the early 1950s, plant-available N was conserved in
the soil through bare fallowing, a practice that depletes organic matter and damages soil structure,
which led to large-scale soil erosion; wheat yields were static at around 0.8 t/ha.
With the introduction of legume-based pastures, yields increased and stabilized at around 1.3
t/ha, due almost entirely to N benefit from legume N2-fixation. Net increments in soil N under the
pasture commonly ranged from 35 to 100 kg/ha depending on productivity of the legume. Soil
structure also benefited, with enhancement in water infiltration and root penetration.
The N2 fixed by legume crops in Australia has an economic value, in terms of both the N itself
and rotational benefits. The value of fixed N in a legume crop can be calculated using an average value
for %Ndfa (the proportion of legume N derived from N2 fixation) and the average yield data.
Much of Asia's population is dependent on rice as the chief source of sustenance, and it has
been estimated that, within the next 30 years, a 65% increase in production will be necessary to meet
the requirements of the growing population. This need forces the development of higher yielding
varieties that will require increased fertilizer inputs. In the face of prices that are currently prohibitive
for growers in much of the developing world, alternatives to synthetic chemical N fertilizers are
needed urgently. Hence, new attention must be paid to exploiting biological sources of N to meet the
requirements of rice and the other important cereal crops. Not only do grain legumes (pulses) provide
a potential source of N in rice-consuming Asia, they are already important as sources of dietary protein.
However, for economic and other reasons, the acreage planted to pulses in that region has been
declining in recent years; the production of cereals is more lucrative for many farmers, hence legume
cultivation is increasingly marginalized to poorly productive soils. Given the potential importance of
the contribution of N as well as being a significant source of food protein, it is important that legumes
be integrated into farming systems, and management practices adopted to maximize fixation and to
optimize the utilization of organic N in stovers applied to the soil for benefits to the production of rice
and other cereals.
Experiments with mung bean in the Philippines demonstrated genetic diversity for
improvement of subsequent maize growth and yield.
Improving the yields of legumes while
maintaining optimum N2-fixing capability, and increasing legume productivity by removing
constraints for the symbiosis, are simple conceptually but not so in practice. The complexity of the
problems involved are indicated in this document. Moreover, pulses in Asia, despite their nutritional
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importance, are grown largely on marginal, impoverished soils. In such conditions, yield potentials are
low and it is likely that N is not a chief growth-limiting factor. Therefore, adopting management
practices to improve the root-nodule symbiosis, e.g. by application as inoculant of a rhizobial strain
found to be superior to indigenous types in greenhouse trials, will have no utility. Only by growing
legumes in fertile conditions, possibly with inputs to raise yield ceilings, then inoculants may have an
optimizing role and only if N is the chief growth-limiting factor. This 5-year programme has shown
that there is a wealth of genetic diversity in the food legume species of importance in Asia in their
capacity to fix N2 and to contribute N for the benefit of non fixing crops in the farming system. The
data herein demonstrate that there is significant potential to exploit the root-nodule symbiosis for
better yields of all components of the cropping systems of the region. There is need to research the
various contributions of legumes within those cropping systems, with long-term experiments so that
cumulative effects may be detected and documented. It is hoped that this document will serve as a
foundation for future work on improving productivity of cropping systems as a whole by maximizing
N2 fixation by its component grain legumes.
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IV.
ALTERNATIVE PEST MANAGEMENT
PESTICIDAL PLANTS
Pesticides are substances or mixtures of substances used to prevent, destroy, kill, control or
mitigate pests. Pesticidal plants, sometimes referred to as botanical pesticides, are naturally occurring
pesticides derived from plants. Pesticidal plants are our oldest form of pest control and take advantage
of a plant’s natural defenses against herbivory developed over millions of years of evolution. Most
plants produce chemicals that deter pests, often producing a mixture of compounds that repel and stop
herbivores from feeding. In large enough quantities these compounds can even be toxic to the
herbivore (Debach, P & Rosen D, 1991).
Pesticidal plants have been used for millennia and were widely used in commercial agriculture
up to the 1940s, when synthetic pesticides were developed. Overuse of synthetic pesticides led to
problems such as environmental contamination, resistance development and health concerns that were
not anticipated at the time of their introduction. Cancer, adverse effects on immune systems,
neurodevelopment dysfunction, metabolic diseases such as diabetes, endocrine system disruption and
infertility are some of the health risks associated with continuous exposure to synthetic pesticides.
At the smallholder farmer level, synthetic pesticides are costly and have limited distribution in
rural areas. Synthetics are often adulterated by dilution, mixed incorrectly and sold beyond their expiry
date. Synthetics can also kill insects which may be predators of some pests, thus causing
environmental imbalances in natural regulation that inadvertently lead to economic loss by
exacerbating pest problems. Over time, and through misuse, pests can build resistance to synthetic
pesticides. This has resulted in the development of pesticide resistance among over 500 insect and
mite species. It is also evident that repetitive use of synthetic pesticides has resulted in pesticide
residue hazards, and this has had a negative impact on ecosystem service delivery of natural enemies,
pollinators and other wildlife, as well as extensive persistent groundwater contamination (Debach, P &
Rosen D, 1991).
Pesticidal plants can potentially surmount the problems resulting from use of synthetic
pesticides. Pesticidal plants break down rapidly with negligible persistent ecological impacts and can
thus provide environmentally-benign pest control. Their impacts on beneficial organisms and other
non-target species is negligible compared to synthetic pesticides and they are equally cost-effective
when compared to the use of synthetic pesticides.
When incorporated into integrated pest management programmes, pesticidal plants could
decrease the need for synthetic pesticides while also being more easily used in combination with other
pest management approaches such as biological control. By cultivating and selling pesticidal plants,
farmers could provide sustainable and environmentally-benign pest management control and boost
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their income. Most Asian countries rely on imported synthetic pesticides and generally are only
involved in re-packaging, marketing and distribution of synthetic pesticides (Sola et al., 2014).
Pesticidal plant compounds such as rotenoids from Derris spp., Tephrosia spp. and
Lonchocarpus spp. have been produced as organic pesticides and used in agriculture and horticulture
worldwide, with some products still registered in some countries. The neem tree, Azadirachta indica is
a popular pesticidal plant used in South Asia and parts of Asia. Other trees species related to neem
such as the chinaberry tree, Melia azedarach, have been developed into commercial products in China
and Southeast Asia. Essential oils, which are complex mixtures of volatile organic compounds often
found in many herbs and spices, also have pesticidal potential and have been commercialized in North
America.
Farmers use pesticidal plants in various ways and in various amounts for different crops, preand post-harvest. For example, for any given pesticidal plant species farmers may report that they use
whole or different parts of fresh plants; whole or parts of dried powdered plant; cold/hot water extracts
poured over, sprinkled or used as dip or placing pesticidal plant material and crops in layers. The
amounts used of fresh or dry material can vary, and sometimes, one or more pesticidal plant species
are extracted and used together. Although there may be good reasons why farmers do things in
different ways, there are also good reasons to try to standardize and optimize the way pesticidal plant
species are processed and applied.
Standard methods can increase reliability and predictability of pest control, as well as help
disseminate knowledge on pesticidal plant use more widely. For example, understanding the chemistry
of pesticidal plants and identifying the active ingredients can reveal if the compounds will be easily
extracted in water. Some compounds will not easily dissolve in water, and the addition of soap during
extraction can help get these more ‘fatty’ compounds to extract, leading to increased efficacy in pest
control.
Risks of toxicity are further mitigated in that the amount of active ingredients naturally found
in parts of plants is often very low and certainly not present in the artificially concentrated amounts
found in synthetic pesticides. Many of the compounds in pesticidal plants are found in food and
medicines, notably herbs and spices from which essential oil pesticides are made, where the USA has
categorized them as GRAS (generally regarded as safe) and not subject to toxicity testing requirements.
It is nevertheless essential to remember that plants contain toxins and to use appropriate safety
measures such as gloves, face masks, protective clothing and exercise caution particularly when
processing plants, e.g. grinding, sieving plant powders and applying them to crops, e.g. spraying,
admixing. Users should avoid inhaling powders or contact with skin and eyes. In case of accidental
contact, the affected area should be washed with clean running water.
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Many plant species have been recognized by farmers as having pesticidal properties. The parts
used include leaves, fruits, seeds, bark, roots and flowers. Most pesticidal plants are collected from the
wild and over-harvesting can lead to biodiversity loss.
Weedy and invasive species are perhaps at no risk of over-collection. However, collecting
some plant parts such as roots or bark from slow growing indigenous trees and shrubs can be
particularly detrimental, thus weakening or killing the plant. In many cases unsustainable collection
methods have already made some plant species difficult to find in the wild. Often, the same plant
species are collected to make traditional medicines, therefore, training guidelines have been produced
on how to sustainability collect wild plants, and we recommend that users of pesticidal plants follow
these guidelines. Furthermore, the sustained availability of pesticidal plants may be maintained if they
are managed, domesticated, conserved and used efficiently, thus helping to meet the needs of the
present and future generations.
Some species such as Tephrosia vogelii and Tagetes minuta are already cultivated and inter
cropped to take advantage of soil improvement properties or repellent properties. Many others can be
easily grown, and even more difficult species can usually be propagated with the right knowledge
provided.
It is important to correctly identify the plants to be used. Often, many species look similar, and
there may be varietal differences that are not easy to tell apart. This can lead to recommending the
wrong species, which does not have the pesticidal chemicals found in a closely related species. It is,
therefore, important that plant specimens are collected and verified by experts. This is done by
collecting herbarium voucher specimens and depositing these in a verified herbarium. Errors in
identification can lead to serious problems of misuse of plant materials.
INVASIVE SPECIES
Care should be taken about the spread of invasive species. Many weedy pesticidal plant
species are found along roadsides and degraded land. In these cases, it is not usually necessary to
propagate and cultivate them because they are already abundantly available in nearby habitats.
Collecting them for use as pesticides may actually be beneficial in helping to control their spread.
However, care should be taken not to actively propagate invasive species and extensionists should
check whether the species they promote are potentially dangerous to biodiversity.
Demand for botanicals is set to grow due to increase in organic farming, consumers
demanding safe food and environmentalists lobbying for eco-friendly pesticides. Unfortunately
pesticidal plant products are not always readily available in the right forms for small scale farmers nor
are there any ready-to-use products. This challenge in itself is an opportunity for small scale farmers to
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increase access and raise the profile of plant pesticides by engaging in low cost processing and
marketing of such products. Thus, as the demand for organic products grow the potential for
marketing and trading in plant pesticide products will also grow (Ghosh G.K., 2000)
However, selling most pesticidal plant products is currently beset with some challenges which
include: lack of data on efficacy, safety, toxicity, persistence, shelf life and safety, inconsistent
performance of crude extracts and inherent differences in plant chemistries, unreliable and or unknown
raw material supply, as well as lack of standardization and documented application protocols.
Legislation in all countries requires that all pesticides including botanicals have to be registered, a
process that requires detailed data. This remains a major constraint to promotion and marketing.
However, successes in some countries like India, Kenya and Tanzania where specific procedures have
been developed for bio pesticide registration has led to remarkable successes in this regard.
Nevertheless, there are already a number of pesticidal plants that have been adequately researched
(neem, pyrethrum, tephrosia) presenting opportunities for marketing and up scaling. For this to happen
there is need to invest in local production and distribution; development of low cost technologies and
value chain development where small scale farmers can play a critical role.
Despite all these difficulties, there are some basic standard methods and ideas that can be
generally applied when it comes to using pesticidal plants. By providing knowledge on the basic
concepts and procedures of using pesticidal plants, farmers can go on to do their own experimentation
to optimize their time inputs and level of pest control desired.
Farmers first need to understand that pesticidal plants usually do not kill insects immediately.
Exposed insects may take a few days to die, or the insects simply leave. Pesticidal plants can be
directly toxic but often act through repellency, antifeedancy, growth regulation or stop insects from
laying eggs. Farmers who are used to the fast effects of synthetic pesticides killing insects may be
disappointed when using pesticidal plants unless they learn how to more carefully observe crop
damage.
Farmers need to observe the effects of pesticidal plant application over longer time periods.
Results may not be as dramatic as experienced with synthetic pesticide use. It is also important for
farmers to understand that we do not have all the answers, but we do have some answers. Farmers
should be encouraged to experiment, e.g. establish efficacy before widely using, and try different
plants, concentrations, or mixing different plant species together to achieve optimal results.
Regardless of what plant part is collected, e.g. flowers, roots, leaves, all materials should be
dried in the shade. This is because exposure to sunlight often reduces efficacy. Once dry, materials
should be stored in dry, dark conditions until ready for use. Shortly before use, grind or pound and
sieve the material to a fine powder.
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Farmers may want to store the material as already ground up powder. However, grinding the
material will speed up oxidation and can reduce the amount of active ingredient if stored for a long
time. Plant materials can be stored as powder, but the time stored as a powder should be limited to, say,
no more than one field cropping season.
Farmers may also ask whether it is acceptable to use freshly collected leaves or other plant
parts. Fresh materials contain a lot of water already, and this can reduce the total amount of
compounds that can be extracted. It is also difficult to grind fresh leaves; these are often pounded into
a mush. This reduces the amount of exposed surface area and the amount of compound that can be
extracted. Therefore, using fresh material makes it more difficult to achieve a consistent product and
efficiently extract the compounds.
However, with some plant species, particularly those which are aromatic and contain volatile
compounds, there may be good reasons for using fresh material. Some volatile compounds will
naturally leave the plant as it dries and it may also be that some compounds are easier to get out of
fresh leaves than with dry leaves. The general recommendation should be to use dry materials,
particularly since many of the plants need to be collected well before the cropping season when they
are available and when farmers have more time. Using fresh material is certainly allowed, particularly
if it is more convenient for the farmer; however, the level of efficacy may differ between using fresh
and dry material.
Adding soap during extraction should be a general rule no matter which plant species or plant
part is used. Soap will help extract any compounds that are not easily water soluble; 0.1% soap is
made by adding 1ml soap per litre. For example, a 10-litre bucket would require 10 ml soap. The soap
also helps spread the extract on the plant leaves more effectively. This is because plant leaves are
slightly waxy and the soap helps the extract to stick to the leaves evenly. If liquid soap is not available,
farmers should be encouraged to use other kinds of soap such as bar soap. In this case, a small piece of
bar soap, e.g. 10g, could be dissolved in a 10-litre bucket. Waste water from cleaning clothes with
laundry soap can also be used (Anjarwalla P. et al., 2016)
To make up an extract for spraying on a crop, add the powdered plant in water overnight to be
used the next day, i.e., let the extract sit for approximately 24 hours in the shade. For a 1% extract, add
10 grams of plant powder per 1 litre water, and for a 10% solution, add 100 grams per litre. Remember
to add soap and the plant powder. This is because the amount of powder will be too much for the
amount of water, thus forming a sludgy mess that reduces the efficiency of the extraction.
Although making extracts at less than 1% may still give some good pest control for some
pesticidal plant species, it is recommended that farmers try to use a concentration somewhere between
1% and 10%. Making a standard solution does not need precise balances and measures. Farmers could
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use a standard cup of powder per standard bucket of water, once the volumes of the containers have
been worked out with extension agents to understand what the approximate concentration will be
using locally available containers. Shortly before spraying, filter the extract through a fine cloth to
remove particles that could clog the sprayer. Particularly if using a sprayer, filter higher concentrations
of 10% solutions twice, once through a rough cloth and again through a finer mesh. Extracts can also
be applied with watering cans or brushes, but sprayers are more effective in spreading the extract
evenly.
Many pesticidal plant compounds break down quickly in sunlight. Thus always spray extracts
during late afternoon or evening to maximize contact time with insects. This rapid breakdown of the
compounds by sunlight means that pesticidal plants need to be sprayed more frequently than
commercial synthetics. Weekly spraying of pesticidal plants has been shown to be as effective as
commonly used synthetics (Mkenda et al., 2015). Although even synthetic pesticides are washed off
by rain, plant extracts will be even more susceptible to wash off, so farmers should reapply the next
day if it rained during the night after application.
Generally, using powders or solid residues obtained after extraction are not easy to use on
field crops as they do not easily stick to the plant. However, they can be used in some circumstances
such as with maize (or millet and sorghum) to prevent stem borers. This is done by sprinkling the
powder on the plant so it gets trapped between leaves and stem.
Smallholder farmers storing commodities at the household level continue to suffer from many
insect pest species that infest their cow peas, beans, maize, millet, sorghum, groundnuts and other dry
grains and legumes. Controlling insect infestation during storage can involve several basic practices
that could dramatically reduce the need for pesticides (synthetic or plant based). Before considering
the use of pesticidal plants in post-harvest storage protection, farmers should first ensure that they are
following good storage practices.
Unfortunately many problems with insects on stored commodities begin in the field at the time
of harvest where some seeds become infested. Since many farmers find it difficult to properly dry their
grain to low moisture content, the insect problem rapidly grows from the initial field infestation.
However, even if grain is clean, dry and free of infestation when stored, it could still become infested
later on through insect invasion, particularly as most on-farm storage structures are not insect-proof.
For these reasons pesticidal plants can be an effective way of reducing or preventing infestation of
stored commodities
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A REVIEW OF IMPORTANT ALIEN INVASIVE SPECIES IN THE PHILIPPINES
According to the Convention on Biological Diversity (CBD), “Invasive alien species are
species introduced deliberately or unintentionally outside their natural habitats where they have the
ability to establish themselves, invade, outcompete natives and take over the new environments”.
They are widespread in the world and are found in all categories of living organisms and all types of
ecosystems. However, plants, mammals and insects comprise the most common types of invasive alien
species in terrestrial environments (http://www.biodiv.org).
In the Philippines, four of the most important alien invasive pests are the golden apple snail,
locally known as golden kuhol (Pomacea canaliculata (Lamarck)), the rice black bug, locally known as
“itim na atangya” (Scotinophara coarctata (Fabricius)), the mango pulp weevil (Sternochetus frigidus
(Fabricius)) and the mango seed weevil (S. mangiferae (Fabricius)).
The golden apple snail and the rice black bug feed on rice. Rice, the food crop for more
than half the world’s population is the staple food in the Philippines. Of the 4 million hectares of total
rice area, the average rice yield in the Philippines as of 2000 was 3.1 metric tons (MT) per hectare
(IRRI, 2002).
The mango pulp weevil, Sternochetus frigidus (Fabricius) and the mango seed weevil, S.
mangiferae (Fabricius) attacked mango fruits of cultivated and wild species in some parts of Asia like
the Philippines (Gabriel, 1977; De Jesus, et al., 2004). Mango is the national fruit in the Philippines
and is the third most important fruit crop of the country based on export volume and value next to
banana and pineapple. Mango export in the country reached to 35,771 MT in 2003 ($31.011 million)
with country’s production of close to one million metric tons (Catindig J.L. & Heong; K.L., 2002).
The Philippine government encouraged its production and sponsored a livelihood project in
1984-85 by distributing the snail to all main islands to be raised in soil pits as a backyard cottage
industry and promoting it as a national livelihood program The urban enterpreneurs were among the
first raisers who were interested in generating additional income.
The snail eventually escaped from backyards and by 1985, GAS was all over the Philippines
and found its way to agroecosystem and started to alarm the rice farmers. Farmers consider the golden
apple snail to be the most serious pest in the Philippines in 1986 (Morallo-Rejesus et al., 1990).
Further, it is said that the population of the native apple snail, Pila luzonica, has declined drastically
since the introduction of the golden apple snail.
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Distribution
Aside from the Philippines, GAS is found in Argentina, Bolivia, Brazil, California, Cambodia,
China, Dominican Republic, Florida, Guam, Hawaii, Indonesia, Japan, Korea, Laos, Malaysia, Papua
New Guinea, Paraguay, Singapore, Suriname, Taiwan, Texas, Thailand, USA, and Vietnam.
Biology and ecology
The golden apple snail is prevalent in wetland such as marshes, swamps, rivers and irrigation
canals lined with vegetation or rice fields. It can survive harsh environmental conditions with
pollutants in the water or low dissolved oxygen levels (CABI, 2001). It can bury itself in moist soil
during the dry season. It aestivates for 6 months then became active again when the soil is flooded
(PhilRice, 2001).
The golden apple snail shell is light brown with creamy white to golden pinkish or orange
flesh (Fig. 1). It has both gills and a lung-breathing organ. It digs deep into the mud and surfaces
again after renewed flooding. During drought, it closes its operculum. It prefers newly-transplanted
rice seedlings up to 15 days after transplanting are vulnerable to golden apple snail damage and from 4
days to 30 days after sowing for direct-seeded rice .Young plants that are soft and succulent are
susceptible because the snail feeds by scraping the plant surface with its rough tongue. It also feeds on
any decomposing organic matter.
The golden apple snail has separate sexes, which can be
morphologically distinguished by the curve of the operculum. The male has a convex operculum while
the female has a concave operculum. The shell of the female adult snail curves inward while the male
shell curves outward.
The average sexual maturity of the golden apple snail is attained in 60-90 d after hatching and
may spawn at weekly intervals throughout the year. Mating occurs any time of the day in all seasons
of the year in places where there is a continuous supply of water. It is prolific and reproduces ten
times faster than the native species. A gravid female snail adult can lay as much as 25-1200 eggs or
25-320 bright pink eggs per week with 80% hatchability.
After hatching, the soft-bodied juveniles drop into the water and cling onto nearby surface.
Their shells harden in 2 days and the hatchlings crawl when they reach 2-5 mm in size (CABI, 2001).
Hatchlings grow and mature fast. They are voracious feeders and grow quickly, maturing at about 2
months old. They have been called “eating machines” because they can eat 24 hours a day. The most
destructive stage is when the length of the shell is from 10 mm or 1 cm (about the size of a corn seed)
to about 40 mm or 4 cm (about the size of a pingpong ball) (Dela Cruz et al., 2000).
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Recent findings in the rice field in La Union, Philippines showed that the golden apple snail
was found to be effective against weeds (http://www.manilatimes.net). It is now consider by farmers
an ally rather than an enemy because it can now manage weeds in lowland irrigated where
transplanted rice is planted. The snail would benefit farmers provided that the field is leveled very well
so that the depth of water as well as movement of the snail could be controlled. No water should be
added to the field after transplanting for four to six days. Water should be released into the field once
weeds have grown to one centimeter. By this time, the rice plants are already 25 to 28 days old and
their stems are already hard. The snail would prefer the soft and succulent weeds.
Pomacea canaliculata is similar to other snails including P. doliodes and P. glauca, which are
pests of rice in Suriname, and P. insularum in South America. It may also be confused with other
snails of the genus Pomacea that are raised for food including P. gigas and P. cuprina which may have
escaped into rice fields in Asia.
Management
There are physical, mechanical, cultural, biological, and chemical control measures
recommended against the golden apple snail. Among the recommended cultural control measures,
crop establishment, planting methods, seedling rate, good leveling the field to remove snail refuges
and facilitate drainage, planting at higher densities, burning straw, are the most used methods. An offseason tillage to crush snails can also be employed. Snails can also be exposed to sun. Draining the
field is also advised (Litsinger & Estaño, 1993). Crop rotation with a dry land crop and fallow periods
is also recommended as control.
Depressed strips can be constructed to retain a small amount of water drainage. This method
also confines the snail to limited areas, hence handpicking can be facilitated. It can be done during the
final harrowing period.The rice black bug or RBB, Scotinophara coarctata (Fabricius) is a dreadful
insect pest in the Philippines. From Palawan, it moved to Mindanao in 1992 (PhilRice, 2000) and the
Visayas region in 1998 and moved back again in Mindanao in 2000 and in the Visayas region in 2001.
Distribution
The rice black bug also occurs in Asian countries such as South China, Vietnam, Brunei,
Indonesia, Malaysia, Cambodia, Sri Lanka, Thailand, Myanmar, India, Bangladesh, and Pakistan
Unlike other pests, which damage the rice plants only at a certain stage, the rice black bug attacks rice
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at all stages of crop growth particularly from maximum tillering to ripening growth stage.
At
vegetative stage, the damage is called deadhearts and whiteheads during the reproductive stage. RBB
can cause plant stunting and bugburn where the leaves turn reddish brown, resulting to crop loss. The
nymphs are the most destructive stage because it feeds at the base of the rice.
Like the adults, the nymphs have similar behavior of remaining in the base of the plant during
the day and feeding at night. The nymphs reached adulthood after 4 to 5 molts in 25-30 days. Rice is
the main host. It also feeds on a number of grasses and broadleaves (PhilRice, 2000).
S. coarctata is similar to many other oval-shaped shield or stink bugs that occur in rice, but the
non-pest species seldom occur in high numbers. S. coarctata is distinguishable from S. lurida by the
position of spines on the pronotum (CABI, 2001).
Management
The best management option for RBB is the possible use of classical biological control. The
egg parasitoid T. cyrus is apparently not found attacking Scotinophara species in the Philippines.
There are other natural enemies that might be of significance.
Sternochetus frigidus (Fabricius) or MPW is a recently introduced insect pest of mango fruits
in the Philippines. Its distribution, however, is restricted to the islands of Palawan. Its establishment in
southern Palawan is attributed to the shipping route and trade activities between southern Palawan and
Borneo, which is a native area of the pulp weevil (Basio et al., 1994). It is considered as one of the
serious problems of the mango industry because its presence brought about a quarantine restriction on
Philippine mangoes, which prevented the opening of new markets for export. To protect the Philippine
mango industry, the Palawan Island group was placed under quarantine through BPI Special
Quarantine Administrative Order No. 20 Series of 1987 (http:www.pcarrd.dost.gov.ph).
Distribution
Aside from the Philippines, MPW can be spotted in mangoes in Northeast India, Bangladesh,
Myanmar, Thailand, Malaysia, Singapore, Indonesia, Pakistan and Papua New Guinea (CABI, 2001).
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Biology and ecology
The adult of MPW is a small hard-bodied insect. It is black with brown patches in the elytra
and legs. Its female adult lays single eggs on a mango fruit when it is about the size of a chicken egg.
Eggs are opaque and turn light yellow with the developing cranium becoming noticeable. The female
later covers the eggs with black sticky exudate, which later turns into brown, dry and hardened egg
plug. This egg plug serves as protection by holding the eggs in place. Eggs are 0.4 mm long and 0.5
mm wide and hatch in 9.3 d. Eventually the neonate larvae enter the young mango fruits by boring
through the soft skin, preferring the area closer to the seed causing the darkening of the affected
tissues.
The mango pulp weevil undergoes five larval instars observed in 20.3 days. Older larvae
create feeding canals or tunnels as they move from one area to another in order to feed. Before
pupation, the mature larvae specifically the 5th larval instar prepares a pupal cell and confines itself to
this pupal cell until it becomes an adult. Development from larva to prepupa to pupa to adult takes
place inside the fruit. The pupa is exarate and active. Total development of S. frigidus from egg to
adult stage is 32 d. The adult remains inside the fruit for another 37 d. It was found out that 70% of
the adults exit the fruit by boring a hole directly underneath the pupal chamber.
The damage caused by MPW is not apparent in infested fruits. By the time, the fruits are
harvested the tiny wound created by the young larvae as their point of entry in the skin of mango fruits
is not anymore recognizable and had completely gone.
In the absence of mango fruits, MPW adults have been found feeding on mango flowers or
panicles during full bloom stage with peak activity observed at 0600-1000h (De Jesus, et al., 2003).
During the fruiting season, the adults also feed on the developing fruits by making very small
punctures on the peel. However, the larvae are the most destructive because they feed and develop on
the pulp.
Management
There are mechanical and chemical control measures available for the mango pulp weevil.
One way of preventing the insects from touching the fruit is to bag it or cover the whole fruit. The
fruits can be bagged when the fruits are the size of a chicken egg or about 55 to 60 d before spraying.
Doing so effectively protects the fruits from pest and diseases. Durable papers such as imported
newsprints are the recommended bagging materials, newspapers or the yellow pages of phone
directories can also be used. Fruit bagging can reduce the use of pesticide by 23% and it reduces fruit
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rejects from 60% to 15% of the total harvest. It was found out that the cost of chemical control with
bagging was P 818.00 a tree, while non-adopters spent P 1,050 a tree.
Pruning is also advisable as it removes unproductive and overlapping branches as well as
those damaged by insects and diseases, resulting in good light penetration and air circulation.
Sanitation is another way of control.
Mango Seed Weevil, Sternochetus mangiferae
Of equal importance is the mango seed weevil or MSW, S. mangiferae. It was first described
in 1775, in the genus Curculio (CABI, 2001). It is also found in the Philippines. On numerous
occasions, it has been intercepted in mangoes from the Philippines by the Animal and Plant Health
Inspection Service of the United States Department of Agriculture. It was known to originate from
India. However, its mode of transfer to the Philippines is not known.
Distribution
The mango seed weevil is found in Asia, Australia, Bangladesh, Barbados, Bhutan, Chagos
Archipelago, China, Dominica, Fiji, French Polynesia, Guadeloupe, Guam, Hawaii, Hongkong, India,
Indonesia, Martinique, Malaysia, Myanmar, Nepal, New Caledonis, Northern Mariana Islands, Oman,
Pakistan, St. Lucia, Sri Lanka, Thailand, Tonga, Trinidad and Tobago, United Arab Emirates, United
States Virgin Islands, Vietnam, Wallis and Futuna Islands (CABI, 2001).
Biology and ecology
Not many studies have been conducted on the mango seed weevil. Its adult lays its eggs in
green fruits. Its legless larvae bore as far as the seed, leaving only a tiny scar on the skin. The larvae
feed during maturation and then bore a second gallery to leave the fruit, enhancing the development of
secondary rot at the end of storage.
The mango seed weevil is similar in appearance to S. frigidus. S. frigidus and S. mangiferae
can be distinguished because the pronotum of S. frigidus is parallel-sided in the basal half; the elytra is
only one quarter as long as it is broad and is strongly declivous apically; the profemora is slender, not
clavate (CABI, 2001). While the use of synthetic pesticides in agriculture might have helped to
increase food production, this has not occurred without great costs to human health, the environment
and natural resources.
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HERBICIDES
The 2017 UN report of the Special Rapporteur on the right to food highlights the adverse
impact of pesticide use on human rights, human health (workers, their families, bystanders, residents
and consumers) and the environment. The report also reveals that intensive agriculture based on
pesticide use has not contributed to reduce world hunger, but rather it has helped to increase the
consumption of food and food waste especially in industrialised countries.
Herbicides have been introduced in agriculture (and horticulture) mainly to combat weeds that
compete with crops for nutrients and sunlight resulting in reduced crop yield and quality. Other
common uses are to eradicate invasive plant species or undesirable plants for livestock farms, to assist
the management of public areas, for aesthetic or practical reasons (e.g. sidewalks, pavements and
railways) or for weed control in private gardens. In Europe, their use in farming has increased
considerably to replace mechanical ploughing, which has been reported to cause soil degradation and
soil nutrient loss, in certain geographic zones with high rainfall and specific types of crops,
particularly in intensive agriculture.
There is an overall erroneous perception that herbicides are safe for human health and have
little impact on the environment. Based on this misconception, humans have developed agricultural
practices and invested in technological development that completely depends on the use of pesticides
and herbicides. Many farmers have abandoned more sustainable farming techniques altogether. As a
result, every day tonnes of herbicides are released into the environment and their surroundings, which
not only put human health at risk, but also interfere with the biological processes of nature and the
ecosystem services it offers to combat weeds and other pests naturally. Weeds become resistant, the
soil get eroded and infertile, the crop susceptible to pathogens and diseases, and farmers feel obliged
to use more pesticides to combat the new pests, and end up trapped in a “pesticide treadmill”.
In a similar manner to other pesticides, herbicide active ingredients are biologically active
compounds. They are designed to pass through membranes and diffuse into the interior of living cells
to exert the desirable toxic action. Because of their properties, when these substances are used on open
fields they will directly affect other non-target species in the area and the surroundings, and through a
cascade of ecological interactions will end up affecting biodiversity. Furthermore, these same
properties may allow them to interact with living cells of animal species including humans and result
in toxicity. Herbicides can also be toxic to soil beneficial microorganisms. causing a decline in soil
nutrients, fertility and defence systems. This has a direct impact on agriculture, where crops depend on
the quality of the soil. Their use has been so -unnecessarily- intensive that these chemicals have caused
a great impact not only on soil health and agricultural production, but also to human health, the
environment and its ecosystems.
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There is an urgent need to develop technological methods of agriculture that do not depend on
pesticide use. Using the popular glyphosate-based herbicides as a reference, the current analysis
presents a wide variety of weed management approaches, where farmers work together - rather than
against - nature and help maintain a high agricultural yield without contaminating the soil, destroying
biodiversity and jeopardising human and environmental health. Since glyphosate-based herbicides are
non-selective and of broad spectrum, the alternative methods presented in this report can also
substitute the use of different herbicide products.
Glyphosate is the active ingredient of the world’s (and EU’s) most used herbicide-products,
the most common of which is known with the trade name Roundup™, manufactured by Monsanto.
Glyphosate became particularly popular globally in the 1990s with the development of Monsanto’s
soybean glyphosate-tolerant genetically modified (GM) crops (Roundup Ready) followed by GM
maize and cotton roundup-resistant crops. However, its application is not limited to GM crops and is
used in all areas of agriculture and weed management (IARC, 2016.)
The herbicide potential of glyphosate (N- (phosphonomethyl) glycine) was discovered by
Monsanto in 1971 and was registered as an herbicide (phytotoxicant) in 19742. Glyphosate causes
plant toxicity by blocking the action of an enzyme (5-enolpyruvylshikimate 3-phosphate or EPSP)
with a key role in the synthesis of amino acids and other essential nutrients for the plant (through a
cascade of reactions known as the shikimate pathway), resulting in plant starvation and eventually
plant death. In fact, glyphosate was patented in 2010 by Monsanto as an anti-microbial agent against
certain pathogenic infections.
Monsanto however is not the only producer of glyphosate. Once its US patent expired in 2000,
other pesticide manufacturers started producing glyphosate-based herbicide products. According to the
Glyphosate Task Force consortium of companies that produce glyphosate-products, glyphosate is now
marketed by more than 40 companies and over 300 herbicide products containing glyphosate are
currently registered in Europe4.
Glyphosate is a broad spectrum, non-selective, systemic herbicide, crop desiccant and to a
lower extent plant growth regulator4. Being non-selective, glyphosate-based herbicides (i.e.
formulations containing glyphosate as active ingredient together with other chemicals) effectively kill
or suppress all types of plants (including grasses, perennials, vines, shrubs, and trees) and are typically
applied on the foliage of the leaves or on the roots or on the soil to prevent weed growth. Glyphosate
has been reported to be effective against more than 100 annual broad leaf weeds and grass species, and
more than 60 perennial weed species.
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In conventional agriculture, glyphosate-based herbicides are mostly applied before crops are
sown to control weeds and their root systems to facilitate the growth of crops. The herbicide-based notillage approach to prepare the land has replaced mechanical ploughing in conventional agriculture,
which has been linked to soil erosion and depletion of soil’s carbon storage (Derpsch, 1998), and is
how glyphosate is most typically used in Europe. Glyphosate is also used as a pre-emergent herbicide
after sowing but before the crop shoots emerge, to prevent weeds from growing. If the crop has been
rendered tolerant to glyphosate for example by GM technology, the herbicide can be used later, postemergence of the crop (all plants including weeds die while
Another use of glyphosate-based herbicides is as crop desiccants to dry down the crops either
before or after harvest. Application after harvest destroys the remaining crops to facilitate their
removal, whereas pre-harvest application is carried out either to dry any green growth that may
interfere with harvesting or in the case of cereals and other grain-crops, to accelerate the ripening
process of the grains. The use of glyphosate as a pre-harvest desiccant has become a very common
practice in today’s agriculture, particularly in regions where humidity levels are higher. However, it’s
the use that leaves the highest amount of pesticide residues and some Member States have strict rules.
All the registered uses of glyphosate in the EU can be found in the glyphosate risk assessment
peer review report of the European Food Safety Authority and a summary is given in Table 1. In the
EU, the maximum amount of glyphosate that can be applied is 4.32 kg of active ingredient per ha
(4.32 kg/ha) in any 12-month period, which corresponds to approximately 12 l of herbicide product.
This is one litre of product per month.
There are no official data on the overall amount of glyphosate used for agricultural or nonagricultural purposes across the EU. A publication in 2016, based on an analysis of U.S. and global
official data or data from the industry gives an overall picture of the agricultural and non-agricultural
use of glyphosate.
By carrying out a search in the scientific literature one can see that exposure to glyphosate
alone and to glyphosate-based herbicides has been associated with a wide range of adverse health
effects in humans, laboratory animals, farm animals and wildlife. What is probably of most concern to
farmers is that certain clinical human studies have shown that workers who had previously used
glyphosate had a higher incidence of non-Hodgkin lymphoma, a rare case of cancer, compared to
those who had not used glyphosate. Other studies from the scientific literature have reported a range of
adverse effects in laboratory animals following exposure to glyphosate alone and glyphosate-based
products: carcinogenic, genotoxic, reproductive, developmental, of endocrine disruption, etc...
Herbicides are applied on open spaces and are inevitably transferred to all the different
compartments of the environment (atmosphere, soil, surface waters and groundwater, sea). Depending
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on their application and biodegradation rate, these chemicals end up contaminating the environment
(soil, water and living organisms) putting its ecosystems at risk.
Glyphosate works against all plant species, it can even kill large trees and may easily destroy
habitats ranging from wild to semi-natural. No other herbicide is so non-selective. Hence, glyphosate
and glyphosate-based herbicides have direct and indirect impact on the environment and its
ecosystems. Direct effects include glyphosate being reported to cause harm in a wide range of
environmental species (e.g. birds, fish, frogs, snails, insects, soil microbes, etc). Indirect effects
include the unprecedented elimination of weeds, which in turn have an effect on agro-ecosystems.
Farmland biodiversity and ecosystem functions such as natural pest control, pollination services and
functional soil structures are increasingly jeopardised by today’s nearly complete elimination of weeds
and wild plants as well as due to species’ intoxication by agrochemicals. This impact on ecosystem
services has a direct economic cost. This ecological disturbance and disruption of ecosystem services
in areas dedicated to conventional farming is also the underlying cause of the huge difficulties
conventional farmers are facing in returning to ecologically friendly agricultural systems (Schütte,
2003).
Glyphosate’s toxic action on the plant also blocks its natural defence mechanism that responds
to infections. Glyphosate has been reported to alter soil microbial communities, for example to
decrease the population of arbuscular mycorrhizal fungi, which facilitates nutrient uptake from the
plant roots. It is also toxic to beneficial soil bacteria, such as those of the Bacillus family that have a
key role in suppressing specific pathogenic fungi, as well as in making the soil minerals available to
plants. Glyphosate has been reported to bind to the soil minerals (manganese, iron, etc.) blocking their
bio availability to the plants. Actually, glyphosate has been characterised to “significantly increase the
severity of various plants diseases, impair plant defence to pathogens and diseases, and immobilize
soil and plant nutrients rendering them unavailable for plant use. Due to these effects and to increasing
weed tolerance and resistance, farmers are obliged to use fungicides and additional herbicides on their
crops, resulting in a much higher ecological impact (Kremer RJ, Means NE. 2009).
Facts on soil contamination by glyphosate:
▪ Field studies show that glyphosate and its degradation product aminomethylphosphonic acid
(AMPA), which is also of toxicological concern, get quickly metabolised by soil bacteria down to
50% in silt/clay soil (9 and 32 days, respectively). The higher the clay content the slower the
degradation rate.
▪ A recent study shows that glyphosate and AMPA are detected in 45% of European soil (300 samples
from 10 European countries) according to a recent study (Silva et al., 2017). These substances are
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strongly (>90%) adsorbed to soil particles but they are not immobilised in soil. On the contrary, they
are transported together with the soil particles through atmoshpere and water, and can be taken up by
living organisms or deposited in rivers and lakes.
▪ Glyphosate may become easily mobile by water in soils high in phosphate. Phosphate in fertilizers
reduces the adsorption of glyphosate to soil particles, increasing the amount of free glyphosate
molecules in the soil, which can then be absorbed by the plant roots, metabolised by microorganisms
or can leach into the groundwater.
Weed management is a big challenge in agriculture and in many cases a complex,
controversial and expensive problem to resolve. The key is to invest in sustainable agriculture systems
that, when practiced properly, not only stop contributing to the exhaustion and destruction of natural
resources, but also prompt an ecologically viable agricultural production model.
Several methods of weed management already exist that farmers can adopt to eventually
withdraw altogether from pesticide use. Even for complex issues, like the use of glyphosate in
conservation tilling to avoid ploughing and “protect” the carbon-storage capacity of agricultural soils,
can be resolved without herbicide use.
What is a weed? With no set scientific definition, it is often described as “a plant in the wrong
place”. In some agricultural systems in the EU, a farmer will pay significant sums to spray with wide
spectrum herbicides, then pay again, often with publicly-funded subventions, to sow the same species
of “weeds”, as wildflower strips fulfilling the same beneficial agro-ecological functions, attracting
pollinators and natural predators of pest insects. Crop losses because of weeds depend on the type of
crop, weed species, location, and farming systems
Research and farming experience show that ploughing and many tillage practices are eroding
the soils, resulting in poorer non-fertile soils with reduced carbon storage sinks. For this reason, many
farmers may use glyphosate instead of tilling - and conveniently to save several hours of labour work.
Recent studies show that, in fact, reduced shallow tilling (limited to 25 cm of soil depth) not only
reduces weed density but is also good for the soil in the long-term (it positively affects soil
communities such as earthworms and mycorrhizal fungi) and therefore it is a good weed management
technique that overcomes the need to use herbicides. When reduced tilling is combined with the use of
green manure to raise nitrogen levels, crop yields can be comparable, while maintaining soil fertility
and its carbon storage capacity high.
Weeds may directly reduce crop yield and quality, and increase harvest costs. The most
sensitive phase of a crop is in its early growth stage, when the plant is young, vulnerable and highly
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dependent on nutrients, light, and water/moisture supply. If it has to compete with weeds at this stage,
the crop may become weak and prone to pest and disease infections. Once the plant has grown, weed
competition for nutrients and water is less of a problem. In these cases, weeds may cause a problem
during harvesting and reduce the crop yield in that way. Nevertheless, it should be noted that the very
concept of a 100% yield is a flawed one as there are so many variables that will prevent 100%
“efficiency”, especially climate and weather events, which can easily shift final results above or below
10% of the forecast.
But in any case, the solution is not to completely eradicate all weeds, as they also play a very
important role in the conservation of soil. According to a 20-year study in Denmark, about 80% out of
a total of about 200 weeds growing in cultivated fields are too weak to compete with the crops and
therefore do not affect the overall crop yield. It is only 20 % that may affect the yield significantly.
“Weeds”, if managed in certain manner, can have a beneficial role by providing biological diversity
and supporting ecosystem services. For example, they offer a habitat for both beneficial bio control
insects and mycorrhizal fungi: they cover bare soil after harvest keeping beneficial soil microorganism
communities alive through their root extenuates of sugars and proteins. Also, the pollen and nectar
from certain weeds helps in maintaining the population of bio control insects and, which are very
valuable for pest control.
Looking wider than just weed control in a more holistic way, another key element is to obtain
a balance between crop and non-crop vegetation to encourage an increase in natural enemies of crop
pests. A successful weed management approach should take into consideration the biological and
ecological characteristics of weeds and understand how their presence can be modulated by
agronomic/agricultural practices. In general, such measures aim at keeping the weed population at a
level which does not result in an economic loss in cultivating the crop or the crop quality.
The first step in sustainable weed management is to integrate different methods to manage the
weeds, each one adapted to the type of weed and type of crop and applied usually in combination, at
specific times during the life cycle of the crop. This is the basis of Integrated Weed Management,
where different management techniques (preventive, mechanical, biological and monitoring) are
applied during the crops’ different stages to achieve healthy, quality crops and good yields. The
compilation of all the available techniques can be seen as a pyramid where each layer provides a list of
methods that can be applied for weed management (many little hammers), where chemical control is
used only as a last resource if all other methods have failed. This report does not cover the option to
use synthetic herbicides; natural herbicides are presented as a non-chemical weed management option
but focus is given to all other methods.
The practices of weed management can be divided in four parts:
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● Preventive and cultural agronomic practices (measures taken to reduce weed germination)
● Monitoring (observation and identification throughout the process)
● Physical control of weeds (mechanical, thermal)
● Biological control
Based on agricultural knowledge, these practices are now also possible in combination with
various high-tech tools such as digital images for automated steering systems, e.g. used for steering
hoes; GPS for electronic mapping of the position of the seeds; weeding devices etc. It must be noted
that these are high-cost, high-technology machinery and tools that most small/medium farmers will not
be able to afford, especially as farm debt is very high. This currently limits applicability for a great
section of the farming community. Depending on the culture and set-up of farming operations, there
may be options to share machinery between farms co-operating together, especially as machinery is
often invented for one or a few specific crops in mind; this specialisation is important to consider in
the shift between continuous year-on-year monocultures and diverse crop rotations.
It is useful to integrate several approaches in weed management because one method is not
enough to control all weeds. This is because:
•
some weeds are ephemeral or with shallow roots and so are easier to control than
others;
•
some weeds are annual and some perennial;
•
some are spread by cultivation, others by wind;
•
some are avoided by using grazing animals;
•
some are very competitive against cover crops.
Prevention is better than cure: it is the most effective method for dealing with weeds. Once a
weed has entered the field, and has grown and established itself, eradication is far more difficult and
time-consuming; not only to successfully remove the weeds but also to prevent them from spreading
further. Several preventive measures may be applied in parallel or at different times. The importance
and effectiveness of the different methods depends to a large extent on the weed species and
environmental or climatic conditions.
The term “cultural control” (or “cultural” agronomic practices) refers to any method used to
maintain field conditions so that weeds are less likely to become established and/or increase in number,
or to strengthen the crops and facilitate them in competing with the weeds. Some methods are very
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effective for a wide range of weeds and during different times of weed growth and therefore can be
used throughout the crop’s life-time. Cultural weed control includes non-chemical crop management
practices ranging from variety selection to land preparation to harvest and post harvest processing.
On the other hand, before selecting which methods to use in weed management, one has to
take into consideration that techniques involving machinery with fuel-powered combustion engines
are based on unsustainable sources of energy and release carbon dioxide into the atmosphere,
contributing therefore to global warming.
The rotation of crops in a specified order in a field is one of the oldest and most effective
agricultural control measures to regulate weed presence, as well as enriching the soil naturally with
nutrients after it is depleted by producing crops, thanks to the nitrogen-fixing properties of leguminous
crops included in the rotation. Crops are planted following a certain rotation cycle; nutrients they leave
in the soil can be absorbed by the next crop. The underlying concept as regards weed control is that by
changing the conditions in the field, one interrupts the growth and reproductive cycle of the weeds and
this inhibits their growth and spread. In this way, crop rotation helps to avoid the build-up of
pathogens and pests that often occurs in monocultures, and can also improve soil structure and fertility
by alternating deep-rooted and shallow-rooted plants. Farmers may also include cover crops in the
rotation under-sown with or immediately after the primary crop, as a preventive method. Cover crops
do not usually provide a marketable yield but may be planted between two crops of interest (cost crops)
to help in weed suppression, enrichment of soil with nutrients, reduced runoff of water or nutrients, etc.
Overall the benefits of crop rotation are to promote pest-suppression, soil and water quality, nutrient
cycling efficiency, and maintain good yield productivity (Snapp et al., 2005).
A traditional element of crop rotation, for example is to plant first legumes and/or brassica
species that leave beneficial nutrients for the next crops. Legumes fix nitrogen, produce high quality
but limited amounts of nitrogen (0.5-4 mg/ha), and enhance beneficial insect habitat. Brassica species
in particular produce glucosinolate-containing residues (2-6 mg/ha) which help suppress plantparasitic nematodes and soil-borne diseases (Snapp et al., 2005). The selection of species to include in
the rotations must take several factors into consideration: the marketing interest, the agricultural cycle
of each crop, cycles of the main weeds to manage, and the pests and diseases to which the crops are
susceptible.
MIXED CROPPING
Mixed cropping, also known as polyculture, inter-cropping, under-sowing or co-cultivation, is
a method that involves planting two or more plants simultaneously in the same field, so that the
properties of one plant facilitate the growth of the other. Benefits of mixed cropping include a
balanced input and output of nutrients in the soil, suppression of weed growth, suppression of insects
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and plant diseases and an increase in overall productivity. Suppression of weed growth can be done
either physically by crowding out the unwanted species by covering all available bare soil, by
encouraging many individuals of the crop plants and by using crop species that cover the soil with
their leaves; or chemically whereby crop plant roots release into the soil chemicals that inhibit the
growth of certain weed species (this is called allelopathy and it can also occur through mulching with
some species). Mixed cropping can also be used in crop rotation.
under sowing is a mixed cropping practice, which involves seeding one or more crops at the
same time as the main crop, but only the main crop is harvested; this leaves the secondary crops
covering the soil, preventing weed establishment. In this case, apart from the benefits of mixed
cropping (e.g. soil enrichment with nutrients) the under-sown crop suppresses weeds through natural
competition and/or root exudation (allelopathy) and reduces or even eliminates the need for additional
weed management. Many successful tests have been conducted with cereal crops (barley, wheat),
maize and soya, using as under-crop legume plants (white clover, subterranean clover, fenugreek, etc).
Competitive cultivars in agriculture are more tolerant to and therefore are affected less by the
presence of weeds. The varieties may vary in their canopy structure and growth mode which gives
them “weed- suppressing” ability.
This is a potentially attractive option for weed control in comparison to other methods,
because there are no additional costs. Such cultivars may be more capable of reducing the fitness of a
weed species through competition for limited resources, may produce chemical extenuates that reduce
weed growth (allelopathy) and therefore reduce the economic burden of weeds by resulting yield loss.
Competitive cultivars can reduce the reappearance of a weed species in the soil’s seed bank and
contribute to medium to long‐term weed management strategies, reducing the pressure to use
herbicides and improving the sustainability of cropping systems.
This technique is a preventive method with the specific aim of reducing weed emergence in
the next crop cycle and minimize overall soil disturbance. It involves preparing the seedbed several
weeks before sowing by allowing weed seeds just below the surface to germinate and cover the bare
soil surface. The emerged weeds are eradicated mechanically with a cultivator before sowing the crop
of interest (preferably a competitive variety). At sowing time, the seed bank of weed species is already
partially depleted and the emergence of these weeds is much reduced. Moist conditions are essential to
encourage weed emergence. The small weeds which germinate are easy to manage and can be
removed with a very shallow harrow or with a flame-weeder.
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MULCHING
Covering or mulching the soil with plant residues/wastes or synthetic mulches is one of the
most popular management practices that reduce weed problems either by preventing altogether weed
seed germination or by suppressing the growth of emerging seedlings. Mulch systems suppress weeds
due to their physical impact by preventing weed seedlings growing by blocking or reducing solar
radiation and by increasing the temperature range on the superficial layer of the soil. As well as soil
temperature and light, mulches also affect the passage of water throughout the soil profile.
Mulches can be natural such as straw, sawdust, weeds, paper and plant residues or even
synthetic. Mulching is used particularly for two reasons: to save water and prevent weeds emergence.
Organic mulches: These refer to mulches that derive from organic material (that decompose) rather
than inorganic material (non-biodegradable). Organic mulches include bark wood chips, leaves, grass
clips sawdust, hulls of plants, crop residues following harvest, as well as weeds removed from the
field.
In addition to the above-mentioned effects on soil temperature and other soil properties, it is
also possible to explore the allelopathic potential of certain species used in weed control. The
inhibitory effect of organic mulch on weeds may be due to both the physical effect of weed emergence
suppression (the reduced passage of solar radiation and temperature range on the superficial soil layer)
and the possible chemical effects arising from allelochemicals released by some crop residues that
may contribute to emergence reduction. Organic mulches are only effective at stopping weeds from
germinating. They are not effective at controlling established, especially perennial, weeds. Therefore,
in order to be mulched, the ground must be completely free of established weeds before applying the
mulch, including dormant perennial weeds.
Synthetic mulches
Plastic mulch is a standard practice used by many farmers to control weeds, increase crop
yield, and shorten time to harvest. There are different weed control techniques and materials that could
be used as synthetic mulches, and are explained below.
Two negative aspects of synthetic mulches come from the partial decomposition of the plastic
particularly into micro-plastic fragments, as either this pollutes the soil, or it is transferred through the
water system to the oceans where it contributes to ocean plastic; in both cases plastics are taken up by
and may damage living organisms. It should be noted that biodegradable mulches can also contribute
to these problems as degradation by soil microorganisms ceases during frozen or anaerobic
waterlogged or underwater conditions.
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Although mulching may be more effective in limiting evaporation and saving soil water in arid
and semi-arid regions, it is problematic especially in wetter, colder climates, as the upper layers of the
soil profile become waterlogged and so the nutrients in the soil accumulate at the very top of the soil
profile; carbon sinking is also concentrated there rather than the organic carbon being spread
throughout the upper horizons. In addition, waterlogged conditions are anaerobic, leading to
prevalence of soil pathogens. These issues are also related to the problems encountered with no-till
systems relying on glyphosate based herbicides.
Soil solarisation (or solar heating) consists of covering (mulching, tarping) the soil with a
transparent polyethylene sheet during the hot season, before crop plantation. It is used successfully in
many countries to control or reduce soil borne plant pathogens, weeds, mites and other pests. Soil
solarisation uses radiant heat from the sun, collected through the polyethylene sheet, to heat the soil to
a temperature (40-55oC) that controls soil the target pests.
The possible mechanisms of weed control by solarisation are (1) thermal killing of seeds, (2)
thermal killing of seeds induced to germinate, (3) breaking seed dormancy and consequently killing
the germinating seed, and (4) biological control through weakening or other mechanisms. The effect of
solarisation is greater at top 5-10 cm layer than at lower layers. This explains the efficacy of
solarisation on weed seed germination and seedling growth.
The major effect of high soil temperature (up to 65oC max) is the killing of the weed seedlings
that germinate under the plastic. Solarisation has not been employed on a large scale in field crops but
is used effectively in high-value vegetable crops. The plastic is removed prior to planting and must be
disposed of—a problem all by itself—but solarisation is successful in nearly eliminating use of
herbicides. Although it has the potential to improve weed management, the costs, compared to other
methods, preclude its widespread adoption in crops other than the ones of high value.
The studies demonstrate the effectiveness of solarisation with vegetables, field crops,
ornamentals, nurseries, and fruit trees against many pathogens, weeds, and soil arthropods, and in
various cropping systems, including organic gardening and farming. The use of solarisation in existing
orchards has been an important improvement and deviation from the standard pre-planting methods.
Plastic sheet colour
Black plastic film mulch is the weed management option of choice for many medium- to
large-scale organic and conventional vegetable farms. The plastic cover is an opaque film that reduces
germination of light-responsive weed seeds; it shades out and physically blocks the emergence of most
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weeds; and can enhance crop growth by conserving soil moisture, promoting soil warming, and
speeding nutrient mineralisation from soil organic matter.
Despite being one of the most used methods used in weed control, here we need to highlight
some disadvantages, mainly because synthetic mulches:
•
are manufactured from petroleum, a non-renewable resource.
•
do not provide organic matter to feed the soil.
•
do not provide as good a habitat for ground beetles, earthworms, and other beneficial species
compared to organic mulches, which aid the through flow and percolation of water.
•
are not aerated, rainfall does not percolate, and require drip irrigation for moisture to reach to
rhizosphere
•
must be picked up and disposed at the end of the season.
•
generate large volumes of plastic waste and plastic fibre (200–300 Kg/ha). These end up in the
soil, rivers, the oceans and/or inside organisms including ourselves.
Despite these drawbacks, many farmers use these mulches because fit well into mechanized,
medium- to large-scale production.
Woven black polypropylene mulches
This type of material provides a durable and effective barrier to weed growth. Often used in
ornamental plantations, woven fabric mulches have found increasing use in commercial horticultural
food crop production (especially berries and other high-value perennial crops) because of their
particular properties. These covers are:
•
Permeable to air, water, and nutrients.
•
Opaque and durable, giving effective weed suppression.
•
Long-lasting, typically 8–12 years. Thus, they are considered more ecological comparing with
other synthetic mulches as do not generate as much waste
The only disadvantage is that the material is heavy and expensive but the cost spreads out over
years' of use. Biodegradable Plastic and Paper mulches: These mulches are the ecological alternative
to the use of synthetic mulches, because they eliminate the need to gather and dispose the dirty plastic
at the end of season.The mulch is biodegradable, therefore no clean-up is required.
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Degradable mulch has to degrade completely in the soil, be entirely composed of constituents
derived from natural resources (bio-based), cannot contain synthetics such as petroleum-derived
ingredients, and must completely biodegrade into carbon dioxide, water, and microbial biomass
without forming harmful residues or by-products.
The disadvantage of these materials is the cost, as they are more expensive than regular plastic
mulches. However, some farmers feel that the upfront costs are compensated by the end of the season
since so much time and money is saved because the mulch requires no disposal.
WEEDS CONTROL
With the necessary preventive measures, weed density can be reduced, but this may not be
enough to provide full protection during the early critical and “sensitive” period of the crop’s life cycle,
when the seeds have just sprouted and are especially liable to being out-competed by faster growing
weed species. Therefore, mechanical methods remain an important part of weed management.
The choice of mechanical weeding method depends in part on practical aspects such as the
crop, the soil type, the price, the operating costs and labour requirements. On small areas or where
sufficient work force is available, hand-weeding remains a possibility, particularly in high value crops;
but on most farms, crops are grown on too large a scale, and labour is expensive and often of limited
availability.
Mechanical weeders range from basic hand tools to sophisticated tractor-driven devices.
Mechanical weed control may involve weeding the whole crop, or it may be limited to selective interrow weeding. Mechanical weeders range from basic hand tools to sophisticated tractor-driven devices.
Some overall disadvantages of the use of mechanical weed control are:
•
Mechanical weeding can affect soil structure; especially with compaction in lower layers,
there may be consequences for soil water infiltration;
•
Mechanical weeding may increase soil erosion;
•
Depending on the method, mechanical weeding may affect aeration in upper soil layers,
potentially causing depletion of soil organic matter content.
Mechanical inter-row weeder. Inter-row weeding takes place once the crop has emerged. In
small farms, this can be done with the use of hand hoes, push hoes and other traditional hand weeding
tools but in larger farms it is often seen as a last resort, due to the intense labour it requires.
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There are many types of mechanical inter-row weeders (finger weeders, plough shares, cover
plates, etc) that are mounted on a main beam (e.g. tractor) and can be used for inter-row weeding,
earthing-up and hoeing for weeds. Finger weeders consist of a turning steel disc with flexible
polyurethane fingers, especially designed to control small and just emerging weeds. Mechanical interrow weeding may be followed by hand weeding to deal with weeds left in the crop row that were
missed by the inter-row weeder. Alternatively, some finger weeder discs mounted on springs can
remove weeds both between and within the crop row. This is effective for bigger crop plants like
cabbages. Leader prongs guide the fingers/brushes around the heads of the crop plants, once the
obstacle is passed the mounted brushes spring back to continue weeding within the row.
Alternatively, hand inter-row weeding may take place using mobile platforms. Hand hoes,
small knives, and fingers all have their place. The platforms are normally mounted on a tractor,
allowing workers to sit or lie down on cushions or slung fabric, and provide protection from the sun,
wind and rain.
Harrows
Harrowing is used for smoothing the soil, and is also a traditional form of mechanical weed
control for dealing with annual and small weeds, but it is ineffective against established deep-rooted
weeds; therefore, it should be used in weed management together with preventive methods. In cereals,
‘blind’ harrowing before crop emergence may be carried out after seed drilling but before the crop
seedlings emerge in order to kill the first flush of small emerging weeds. The most common types are
spring-tine, disk, chain or drag harrows. The aim is to give the crop an early advantage over the weeds
to aid selectivity in subsequent harrowing operations.
Tractor hoes
Tractor hoes have ‘A’ or ‘L’ shaped fixed, vibrating or revolving plough shares that undercut
weeds by passing through the soil at 2-4 cm depth. Soil structure is a critical factor as in rough clay
soils, weeds may continue to grow in the lumps of soil lifted by the hoe. Tractor hoes work best in dry
conditions as wet conditions after hoeing may stimulate weed regeneration. Hoeing is particularly
effective against mature weeds. Hoeing with harrows in the upper soil surface, between the crop rows,
is a common practice often resulting in high weed control efficacy
A major disadvantage of hoeing is the relative low driving speed and the limitations of the
fixed tool width resulting in low labour efficiency. Tractor hoes can only be used in crops that are
planted with a relatively large distance between the rows. Another limitation of weed hoeing is the
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limited efficacy of weed control in the infra-row area. New technologies have been developed to
automatically steer hoes close to crop rows using imaging and Global Navigation Satellite System
(GNSS) technologies. These technologies have been applied in maize, sugar beet, soybean and several
vegetable crops. Using digital image analysis, weeds are distinguished from the crop based on shape
features and selectively removed.
Brush weeders
The brush weeder, or brush hoe, is primarily intended for inter-row weeding of vegetable
crops such as carrots, onions and beetroot, although it has also been tested in cereals with very good
results. When used in leafy vegetables there is a greater risk of crop damage.
As the name suggests, the weeding action comes from strong nylon brushes that rotate and
brush the weeds onto the soil surface, pulling out the weeds with shallow ephemeral root systems or
breaking and flattening more robust weeds. Thus, the advantage over the tractor hoe is that it can be
used under more wet soil conditions as well. A second person, in addition to the tractor driver, or some
form of self-steering mechanism is needed to ensure careful guidance of the brushes between the crop
rows.
Cover crop rolling is an advanced no-till technique. It involves flattening a high-biomass cover
crop to produce a uniform mat of mulch. The crop of interest is then sowed through the mulch into the
underlying soil. Attention should be given, because if the right kind of roller is not used on the right
cover crop and at the right time, the rolling process itself will kill or partially kill the cover crop. As
discussed above, care should be taken so that the mulch layer is not too thick, otherwise the underlying
soil may become waterlogged and anaerobic in wetter climates.
Rolling is useful for eradicating weeds before they set seed in stands of high-biomass cover
crops. Uniform stands are important for uniform mulch thickness. In the right climatic conditions, this
practice maximize the amount of organic matter that is deposited back in the soil by a cover crop. The
mulch that is produced also has a positive effect as weed control, and improves moisture retention in
more dry and arid climates and protects soil from rainfall impact and erosion.
Thermal weed control is used in pre-emergence or localised post-emergence of weeds, in
combination with preventive methods, and as the name suggests, it eliminates the weeds by burning
them. Stubble burning is now almost banned because of the smoke and other hazards, but this
traditional form of thermal weed control was frequently used to reduce the number of viable weed
seeds returning to the soil after cereal harvest. Current methods of thermal weed control use a variety
of energy sources to generate the heat needed to kill weed seeds and seedlings.
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Flame weeding is probably the most popular methods of direct weed control after mechanical
weeding. Weed burners or flamers are blowtorches adapted to deliver flames to ground level. They do
not have to burn the plants to ash as long as the heat ‘cooks’ the leaves. Flamers work best on small
weeds with high moisture content because the plant doesn't have the resources to regrow after the
leaves are dead.
The main fuel used in the burners is liquefied petroleum gas (LPG), usually propane. Some
concerns have been raised about using a finite resource as fossil fuels, however alternative fuels such
as hydrogen can also be used. Costs of materials may also be an issue. Flame weeding can be faster
than hand-weeding, but the cost of the machine is higher. Overall treating an area of 6-20 hectares
would bring costs down to a reasonable level but for smaller areas it will depend on the cost of the
crop.
In weed management the use of pre-emergence flaming followed by post-emergence brush
weeding or hoeing have been reported to give promising results. One disadvantage is the impact it
may have on non-target organisms, which has not been fully investigated. But the soil temperature at 5
mm distance depth is raised by 4 °C and at 10 mm by 1.2 °C, and therefore the impact on deeper soil
microorganisms is low.
Steaming is traditionally used in glasshouses to sterilise the soil and control both weeds and
diseases prior to crop establishment. However, now it is also used as an inter-row weed-management
method during the crop growing cycle. Steam is applied under pressure beneath metal pans forced
down onto freshly formed beds for periods of 3-8 minutes. The steam raises the soil temperature to 70100 °C killing most weed seeds to a depth of at least 10 cm. It is also possible to use jets of steam to
kill emerged weeds.
Until recently most thermal weeders were based on gas powered burners. The best designs
generally use ‘liquid’ rather than ‘gas’ phase burners as these are much less prone to pressure-drops
and they incorporate a shroud or hood to retain heat and protect the flames from wind.
Steam has a number of advantages over flame weeders, in that steam is much more efficient at
conducting heat, has better penetration into foliage, operates better in windy and wet conditions, is
safer and some machines can be used to weed over plastic and even paper without causing damage.
Steaming practices however, decrease the abundance of soil microorganisms and studies show
that soil communities may recover but their structure may remain affected for at least 2 months
following the steaming. This should be taken into account prior to the selection of this method.
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Steaming has been used successfully to eradicate the strong perennial weed Cyperus
esculentus in vegetable fields in Switzerland, which could not be efficiently controlled with other
methods, including herbicides.
Hot water
Hot water can be applied with specific machines that keep the water at a temperature over 80
degrees Celsius. Hot water is applied directly on the weeds of interest in the spot where they grow.
Productivity of this method is twice as much as manual removal, and the costs are only
slightly higher. With hot-water treatment there is no need to transport roots away from the site and one
avoids having holes in the grass sward. However, there is still some energy consumption, together
with exhaust and noise emissions. A study carried out on hot water treatment of the common broadleaved dock (Rumex obtusifolius) showed 80% success in eradicating the weeds and 1 year after
treatment there was no evidence of lasting damage to the soil structure on the site, neither did the
treatment stimulate the germination of any great number of dock seeds found in the soil.
Despite not being widely used, there are a few more thermal methods of weed control, such as
freezing, electric currents, irradiation, microwave radiation, and ultraviolet light, among others.There
are some promising new and non-traditional measures that could be used for controlling weeds in
organic farming. New and non-traditional weed control methods such as, infrared radiation (IR), lasers,
microwave radiation, ultra-sonic weed control systems, real-time intelligent robotic weed control
systems and electricity could be used for weed control under field conditions. However, several of
these methods are still under development or are used in small areas.
Finally, it can be concluded that successful and sustainable weed management systems are
those that use integration among techniques rather than depending on a single method, in line with the
“many small hammers” approach of integrated weed management. Further research is needed for new
technologies and methods for weed control in sustainable agriculture.
Monitoring is the key procedure for successful weed management in sustainable agriculture. It
starts with planning ahead before the crop is sowed and is carried out throughout the life cycle of the
crop. During the preparation of the land and crop’s growth cycle, monitoring helps the farmer to detect
the weeds early, identify their type and location, and select what type of mechanical intervention is
necessary, if at all, to remove them or prevent their growth and spread, based on knowledge and
expertise. For example, perennial weeds are more vulnerable to control at the early bud stage or during
fall when the plants begin to go dormant. Mechanical weeding at these stages will be effective. A
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balanced integration of preventive methods, mechanical methods and monitoring (many little hammers)
is key to a successful weed management.
Through monitoring, the farmers also build up their knowledge in relation to the weeds they
have to manage, the efficacy of the weed control methods they have applied (preventive and cultural,
mechanical, biological, even chemical), the impact on the type of crop, and beneficial non-target
species, etc. Then they can apply this knowledge in planning ahead for the next season or the next crop
of interest.
Biological control involves using living organisms, such as insects, nematodes, bacteria, or
fungi to reduce weed populations. In weed management, biological control should be integrated with
cultural practices such as tillage and crop rotation.
The mode of action of the biological control method depends on the selection of the organism.
Fungi or insects that attack seeds can reduce the number of weed seeds stored in the soil, which in turn
can reduce the size of future weed populations. This in turn lowers the effort needed to control the
remaining emerging weeds. Some bacteria live on root surfaces and release toxins that stunt root
growth. Many fungi infect roots and disrupt the water transport system, which reduces leaf growth.
Beneficial insects and nematodes feed directly on the weed roots causing injury which allows bacteria
and fungi to penetrate. Biological control methods have been successfully applied in some parts of the
world, but not so much in Europe.
However, the application of biological weed control is dangerous, as it may introduce
accidentally a tolerant ‘invasive’ species, and must be done very carefully. If not, the introduced
species may spread beyond the targeted area and become a threat to other species, including other
crops of interest.
Nevertheless, only a very small number out of the more than 100 organisms released for bio
control of weeds worldwide have become pests. But it can happen and can have a major ecological
and commercial impact. For this reason, it is imperative that comprehensive ecological studies are
carried out, and indeed enough research funding is provided for researching biological control
methods as alternatives to synthetic chemical inputs.
To date, few weed species can be controlled effectively by weed species’ specific pathogens,
but there are good opportunities for classical biological control of weeds to be developed for Europe as
well.
Animal grazing is another popular method for physical control of weeds, used in parallel with
other methods in weed management. Cattle, goats, sheep and even horses can be used for weed
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management, considering of course that there is an availability of animals and that some adjustments
on grazing time and area are necessary.
Pigs are very good in controlling the growth of weeds and grass, and cleaning up dropped
apples in orchards, and therefore are commonly used for vegetation control in organic orchard systems.
“Sheep weeders” are becoming more popular in different parts of the world due to their low
cost compared to manual labour and their ubiquity. Sheep grazing can be beneficial in vineyards not
just for removing the weeds and machine-mowed grass and canopies, but also because sheep dung is a
good fertiliser for the soil. Sheep should be controlled not to eat the ripe grapes, and one way to do this
is protecting the vines with a net.
Natural herbicides are ingredients extracted directly from plants or animal as opposed to being
produced synthetically. Being natural, they are biodegradable and leave no residues in the soil but they
are not specifically targeting the weed, which means that they will affect other non-target species as
well. Thus, natural herbicides have to be used only when and only when all other methods have failed
as they are also considered chemical solutions in integrated pest management, albeit being natural
chemicals .
Acetic acid, citric acid, clove oil and maize gluten meal all have great potential as nonsynthetic herbicides for controlling weeds and are used in natural-herbicide products available on the
market.
Other classes of natural herbicides are Cinmethylin, a natural herbicide produced by species of
sage, which kills several annual grasses and suppresses some broad-leaved weed species; and the
aqueous leachate of fresh leaves of Eucalyptus globules which significantly suppresses the
establishment of vegetative propagules and early seedling growth of the weeds.
In cold northern European climates, the perennial weed E. repens poses a significant problem
to farmers. How to control this perennial (especially) in organic farming, without making use of
herbicides, while maintaining good soil conditions and trying to prevent it from re-surfacing? Ideally,
by eradicating the perennials mechanically over the post-harvest period; however, this is incompatible
with the use of cover crops to improve soil quality and prevent soil leaching over the same postharvest period.
A new concept is presented comprising in “the uprooting and immediate removal of vegetative
propagules of E. repens located within the plough layer to allow for quick re-establishment of a plant
cover” concerning the issue of dealing with the perennial weed E. repens in the context of cold and
wetter northern European climates.
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The study provides a good example of a field experiment where weed growth in a barley crop
was substantially reduced (by integrated weed management approach) through the use of conventional
practices such as stubble cultivation, combined with varying rotary cultivation (one, two or four passes)
and cover crops (none versus a rye-vetch-mustard mixture). The removal of E. repens rhizome, shoot
growth and suppression was examined in two growing seasons.
Over time, the transition towards lower-impact systems and less reliance on glyphosate could
also become a multiplier for the local economy, engaging local enterprises, ensuring locally adjusted
solutions at hand as leading to increasing value of local knowledge, and making farmers develop more
mechanical skills. Concerning the approach to farming, it will be crucial for farmers not only in
replacing glyphosate by using mechanical means or other less harmful herbicides as a last resort, but
also to re-discover organic farming cycles and techniques, working with nature again, following the
guidelines of the “many little hammers” which over time will increase farmers' resilience while
allowing for a decrease in expenditures for expensive inputs.
PREDATORY BUGS
Although “bug” is often used to describe just about any insect, its correct use is reserved for
the “true bugs,” an enormous group of both herbivorous and carnivorous insects that are characterized
by having a syringe-like beak. Stink bugs, damsel bugs, big-eyed bugs, assassin bugs, ambush bugs,
plant bugs, and minute pirate bugs may all be found in Pacific Northwest gardens feeding on plant
pests like leafhoppers, scale insects, thrips, aphids, psyllids, whiteflies, mites, and small caterpillars.
Predatory true bugs are all generalist feeders and may eat some beneficial insects, but their positive
impact on garden pests far outweighs this negative aspect.
Stink Bugs
Stink bugs have a shield-shaped body and range in size from ¼ to 1 inch long. They usually
discharge a disagreeable odor when handled. Although plant-feeding stink bugs are more common, a
number of species of predatory stink bugs may be found in gardens including the cryptically colored
rough stink bug. Like many predatory bugs, the rough stink bug may feed occasionally on plants, but
does not cause noticeable damage or injury. Until recently, the Pacific Northwest was fortunate in not
having any stink bug species capable of causing serious damage to plants or crops. Unfortunately, the
invasion of the marmorated Asian stink bug (Halyamorpha halys), which is very similar in appearance
to the rough stink bug, has changed this. Identification should be sought for any stink bug found in the
garden before encouraging its persistence.
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Damsel Bugs
Damsel bugs are slender insects up to a ½ inch long with an elongated head, long antennae,
and enlarged front legs for grasping prey. They are mostly yellowish, gray, or dull brown ( 4).
Nymphs look like small adults but are wingless. Adult damsel bugs overwinter in ground cover, debris,
and other protected sites. They emerge from hibernation in April or May and begin laying eggs soon
after. Numerous overlapping generations occur during the spring and fall. Both adults and nymphs
feed on many soft-bodied insects and mites, including aphids, leafhoppers, small caterpillars, thrips,
and spider mites.
Big-eyed Bugs.
Big-eyed bugs are oval, somewhat flattened, and 1/10 to 1/5 inch long. They have a wide head,
prominent, bulging eyes, and short antennae with an enlarged tip. They are usually gray-brown to
blackish. Big-eyed bugs walk with a distinctive “waggle” and emit an unpleasant odor when handled.
Eggs are laid near potential prey and hatch into nymphs that resemble small, wingless adults. Under
summer conditions, big-eyed bugs go through five nymphal development stages (from egg to adult) in
approximately 30 to 40 days. Two to three generations of big-eyed bugs occur each year between
April and September, and adults will overwinter in leaf litter or under bark. Both adults and nymphs
are predatory and prey on a wide variety of insects and mites that are smaller than themselves.
Nymphs may consume up to 1600 spider mites during their development, and adults feed on 80 to 100
mites per day. They also feed on eggs and small larvae of cutworm moths and other caterpillar pests,
as well as all stages of leafhoppers, thrips, and mites. While they are predatory in nature, they can
survive on nectar and honeydew when prey is scarce.
Assassin Bug
The assassin bug is larger than other predatory bugs (2/5 to 4/5 inches long), and has a long,
narrow head with round, beady eyes, and an extended, three-segmented, needle-like beak ( 6). The
front legs are enlarged for grasping prey. It can range in color from black, brown, or red. Its eggs are
reddish-brown, bottle-shaped, and laid in a batch (or “raft”) of 10 to 25 or more ( 7). The eggs are
coated with a sticky substance for protection. Nymphs are slow to develop and early instars are often
ant-like; however they do resemble small versions of adults.
Assassin bugs are long-lived predators (often living more than one season) and consume large
numbers of small insects and mites during their lifetime. Population densities of assassin bugs are
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usually low, but they provide useful, consistent, and long-term feeding on leafhoppers, beetles and
caterpillars in gardens.
Ambush Bugs
Ambush bugs are closely related to assassin bugs but are smaller (1/2 inch long) and specialize
in preying on insects that are visiting flowers. They hide within the flower and kill unsuspecting wasps,
flies, bees, and butterflies. However, immature ambush bugs live on other parts of the plant and
contribute more to the garden pest control effort by eating small, soft bodied insects and mites.
Mirids
Mirids (“plant bugs”) are small, ¼ inch long, and black or brown in color. They are similar to
big-eyed bugs, but without bulging eyes. Some species of mirids are omnivorous, feeding on plants as
well as insects, but they rarely cause significant plant damage. Like big-eyed bugs, they are long-lived
and spend their time hunting for mites, thrips, insect eggs, leafhoppers, and small caterpillars on leaves,
buds, and flowers. The most common beneficial mirid found in eastern Washington is Deraeocoris
brevis. This shiny black bug has pale markings on an oval body that is 1/10 to 1/5 inches long, and
approximately 1/12 inch wide.
Deraeocoris overwinters as an adult in protected places such as under bark or in leaf litter. The
adults emerge from hibernation in March and April and initially feed on the nectar of willow catkins
and other early spring flowers. They seek out prey and begin to lay eggs in late April or May. The first
generation of nymphs appear two to three weeks later and will continue to develop through five stages
in approximately 25 days (at 70ºF). A female mirid can lay up to 250 eggs during her lifetime.
Nymphs have dull, red eyes and are a whitish-gray color with long gray hairs on the thorax
and abdomen—dark patches on the thorax and abdomen give it a spotted appearance. A cottony
secretion covers most of its body. Deraeocoris adults and nymphs are voracious predators—adults can
consume 10 to 20 aphids or mites a day; while nymphs can eat 400 mite eggs per day.
Minute Pirate Bugs
Minute pirate bugs are common predators in gardens and contribute significantly to the control
of spider mites, rust mites, aphids, leafhoppers, mealybugs, and thrips. They are 1/12 to 1/5 inch long,
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oval-shaped, and black or purplish in color, with white markings on the forewings that extend beyond
the tip of the body
They are fast-moving, wingless, and teardrop-shaped. The development period from egg to
adult, through five nymphal stages, takes a minimum of 20 days. Minute pirate bugs are efficient at
locating prey and are voracious feeders—adults and immature nymphs can consume 30 to 40 spider
mites or aphids per day. When prey is not available, minute pirate bugs are able to survive on nectar,
pollen, and plant juices. They aggregate in areas of high prey density and increase their numbers more
rapidly when there is an abundance of prey.
Beetles are the most diverse and numerous group of insects worldwide. This group includes
some very important garden predators, such as ground beetles, and the very familiar lady beetle.
Ground Beetles
Ground beetles (carabids), as their name suggests, are ground-dwelling and live in soil and
detritus. Some species prey on cutworms, ants, maggots, earthworms, slugs, and other beetles.
Carabids are largely nocturnal and are rarely seen, but large populations can exist in gardens and
provide valuable pest control services. There are many species of ground beetles ranging in size from
1/8 to 1 inch long, and most are a shiny, dark color with prominent eyes and thread-like antennae.
Rove Beetles
Rove beetles are common in most gardens, but are rarely seen because of their secretive and
nocturnal behavior. However, if you turn over a rock or log, especially near a compost pile, you will
frequently find these fast-moving beetles. They are odd-looking, shiny brown or black beetles, 1/4 to 1
inch long, with elongated bodies and short wings. Rove beetles have long sharp mandibles that close
sideways across the front of the head, and larger species are capable of inflicting a bite if roughly
handled. They look fierce because of the scorpion-like way they hold the tip of the abdomen, but most
are only dangerous to the insects on which they prey. Adults and larvae feed on a wide range of insects
that are smaller than themselves, especially fly maggots, ant larvae, mites, and many other soft-bodied
arthropods.
Lady Beetles
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Lady beetles are revered for their splash of color, and are a favorite with gardeners and
children alike. After butterflies, they are probably the best-loved insects of all. They are often featured
in human cultures as symbols of good luck and religion—they are certainly a good sign in the garden,
indicating a healthy environment. Lady beetles are industrious predators and are extremely important
to the natural suppression of aphids, leafhoppers, mites, thrips, scale insects, mealybugs, and insect
eggs. Gardeners should encourage all lady beetles to colonize and reside in their gardens. Attracting
and conserving lady beetles is more effective and sustainable than introducing purchased lady beetles
to the garden. Purchased insects tend to rapidly leave the garden after release.
There are about 90 species of lady beetles in the Pacific Northwest, but only a dozen species
are likely to turn up in the garden. The five species most likely to be seen in Washington gardens
include the transverse, convergent, seven-spot, multi-colored, and mite-eating lady beetles.
Transverse Lady Beetles
Transverse lady beetles (Coccinella transversoguttata) are native to North America, but appear
to be declining in numbers (Marshall, 2006). The transverse lady beetle has a round shape and is
approximately 1/4 inch long. Its wing covers (elytra) are orange-red with distinct, narrow transverse
black markings. The body and pronotum (the area between the head and wing cases) are black with
small white or yellow patches.
Females lay yellowish-orange, elongated eggs in upright batches. Eggs hatch into alligatorshaped larva that are purple-blue with orange markings. Larvae molt through four instars before
pupating, and the entire lifecycle, from egg to adult, takes approximately 3 to 4 weeks during the
summer. Both larvae and adults are voracious feeders—adults may consume up to 100 aphids or mites
a day depending on the temperature. When prey is scarce, adults can survive on nectar, honeydew, and
pollen (but will not reproduce).
Convergent Lady Beetles
Convergent lady beetles (Hippodamia convergens) are a native species and are common in
gardens. They are also available commercially and can be purchased from garden centers and
introduced into the garden. However, these ladybeetles frequently disperse away from the site of
introduction.
The adult is approximately 1/4 inch long and more oval-shaped than round. The wing covers
range in color from orange to red and typically have 12 to 13 black spots. However, the number of
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spots is variable, and some individuals have none. The pronotum is black with two converging white
stripes and white edges. The small head is nearly covered by the front of the thorax.
Females will lay 200 to 500 eggs during their lifetime, which hatch in 5 to 7 days. The
alligator-shaped larva is dark gray to blackish-blue with two small, indistinct orange spots on the
pronotum and four larger spots on the back. The pupa is orange and black and is often attached to the
upper surface of a leaf. The insect’s development through larval and pupal stages takes 3 to 6 weeks,
depending on available food and temperature. There can be one to two generations a season, but the
largest populations occur during spring.
Convergent lady beetles tend to disappear when the weather becomes hot, especially in eastern
Washington. Field evidence suggests that populations migrate to cooler, high-elevation areas in
summer and aestivate (go into summer dormancy).
Congregations of millions of inactive convergent lady beetles may be found during July and
August in the Blue Mountains of northeastern Oregon and southeastern Washington. Most of these
beetles overwinter in the mountains before migrating back to the valley areas in spring.
Asian Lady Beetles
The exotic, multicolored Asian lady beetle (Harmonia axyridis) is considered to be primarily a
forest-dweller, but it is frequently seen in home landscapes, and is often the most common lady beetle
species present. There is concern that this species is displacing native lady beetles in some areas of the
United States (Marshall, 2006).
Adults are distinctly oval and convex, and approximately 1/4 inch long. They vary greatly in
color and pattern, but most commonly, they are orange to red with many spots or no spots at all. Some
individuals are black with several large orange spots. The first section between the head and thorax is
straw-yellow with up to five black spots; or it may have lateral spots usually joined to form two curved
lines, an M-shaped mark, or a solid trapezoid.
Unmated females overwinter in large congregations, often in buildings or caves. Mating
occurs in spring and eggs hatch in 5 to 7 days. Asian lady beetle larvae are elongate, somewhat
flattened, and adorned with strong round nodules (tubercles) and spines. The mature larva is strikingly
colored, black to dark bluish-gray, with a prominent bright yellow-orange patch on the sides of
abdominal segments 1 to 5.
In summer, the larval stage is completed in 12 to 14 days and the pupal stage requires an
additional 5 to 6 days. In cool conditions development may take up to 36 days.
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Adults may live for 2 to 3 years and are voracious predators, feeding on aphids, scale insects,
insect eggs, small caterpillars, spider mites, and leafhoppers. In late summer and fall, populations may
increase to high levels, and can be seen swarming on fences and walls. To date, populations in the
Pacific Northwest have not reached the extraordinary levels seen in some areas of the eastern U.S.,
where the insects often enter houses and need to be controlled. While some home invasions have
occurred in the Seattle and Portland areas, it’s been relatively small-scale compared to the eastern U.S.
Seven-Spotted Lady Beetle
The seven-spotted lady beetle (Coccinella septempunctata) is another exotic species, and is a
relative newcomer to the Pacific Northwest, having been unknown in the region before 2000 (Marshall
2006). This lady beetle is large (approximately 3/8 inch long) compared to other lady beetles, with a
white or pale spot on either side of the first section between the head and thorax. The body is oval and
domed. The black spot pattern is usually cond with one spot near the head, four spots across the midsection, and two near the back, on orange or red wing cases.
Adults overwinter in protected sites, and throughout the spring and into early summer, females
may lay from 200 to more than 1,000 eggs. The eggs are usually deposited near prey, in small clusters
of 10 to 50, in protected sites on plant leaves and stems. Larvae are alligator-like, dark gray with
orange spots on body segments 1 and 4. They grow from 1/25 inch to 3/8 inch long in 10 to 30 days,
depending on the food supply of aphids. The pupal stage lasts from 3 to 12 days depending on
temperature. Adults are most abundant in mid- to late-summer and live for weeks or months,
depending on the availability of prey and time of year. One to two generations of seven-spotted lady
beetle occur before the adults enter hibernation.
Mite-Eating Lady Beetle
The mite-eating lady beetle, Stethorus picipes, is a native species commonly found in the
garden; however, the introduced species, S. punctillum, may also turn up. Both species are voracious
spider mite feeders (consuming 50 to 75 mites per day), and are very useful for good biological control
of spider mites. One or two in the garden are usually sufficient to control an early-season mite “hot
spot,” preventing it from spreading into a larger outbreak.
Mite-eating lady beetles are the size of a pin-head (1/25 to 1/16 inch), shiny black in color,
oval, convex, and covered with sparse, fine, yellowish-to-white hairs. Non-reproductive adults
overwinter in protected habitats, such as in ground debris or under bark. Adults emerge from
hibernation in March and April, and begin to seek out spider mite colonies—which they are able to do
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extraordinarily well. Once the food source is located, females feed rapidly (exterminating small
colonies of mites) and lay approximately 15 eggs per day. The eggs are white and laid singly, usually
on the underside of leaves near the primary vein, and adhere tightly to the leaf. A newly hatched larva
is gray to black, and has many long-branched hairs and black patches. The larvae grow from 1/25 to
1/16 inch long, becoming reddish as they mature, just prior to pupation. Larvae develop through four
instars, pupating after 12 days. Pupae are black and flattened, somewhat pointed on the posterior end,
with the entire body covered with yellow hairs. The development from egg to adult takes
approximately 3 weeks, and 3 to 4 generations are produced during the spring and summer months.
Adults live for 4 to 8 weeks during summer and thrive at temperatures between 68ºF and 95ºF.
Scymnus Beetles
A number of Scymnus beetles (Scymnus spp.) are found in Washington, and all are predators
of rust and spider mites, as well as leafhoppers and mealybugs. Adult scymnus beetles are slightly
larger than the mite-eating lady beetle and have similar coloring, making it easy to mistake one species
for the other. However, scymnus larvae are very different. The scymnus beetle larvae have white or
pale colored, long, thick, cottony filaments adorning the body. They look a little like mealybugs and
can be mistaken for that pest.
Earwigs
Earwigs are so named because of their alleged behavior of frequenting people’s ears! This
may have occurred 500 years ago, when people slept on the damp ground (where earwigs live), but the
ear of a twenty-first century human is unlikely to be the dark, damp place an earwig would call home
today. The introduced European earwig (Forficula auricularia) is found in most gardens, and is an
omnivore that eats small insects (especially aphids and small caterpillars) as well as flower petals and
leaves. The earwig is about 1/2 inch in length and is nocturnal. At moderate population levels, the
earwig probably does far more good than bad in most gardens.
Lacewings
Green lacewings lay their eggs singly, each on a long, hair-like stalk, presumably to keep the
egg away from substrate-based predators. Although adults of some lacewings are predatory, it is the
lacewing larvae that provide most of the pest control in the garden.
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Lacewing larvae, like lady beetle larvae, resemble little alligators, but differ by having
enlarged sickle-shaped mouthparts that extend forward from the head. These mouthparts puncture prey
and suck out bodily fluids. A garden abundant with lacewings is almost certain to have a wellbalanced habitat, since these predators thrive best in undisturbed, pesticide-free environments.
Snake flies
Snake flies are similar to lacewings but have an extended “neck” and a long, tapering head,
which resembles a snake’s head. They are about 3/4 inch long and are commonly seen in gardens and
in trees. Snake flies are voracious predators, and feed on a variety of small soft bodied insects and
mites. Larvae are also predatory and can be found living under tree bark or on the ground in decaying
matter.
Predatory Flies
Most people do not consider flies to be beneficial insects, but a surprising number of these
two-winged insects provide good pest control in the garden.
Ants
Every home garden has ants, and, like spiders, these creatures engender fear and loathing in
some people. Ants indoors are clearly a problem, but outdoors, they have an important place in the
garden’s ecology. Many species play an important role as pest control or scavengers. Other species
prefer to collect sweet substances, like honeydew, produced by some pest insects like aphids. These
ants “protect” honeydew-producers from their natural enemies and therefore disrupt biological control.
Fortunately, in the Pacific Northwest, predatory ant species tend to outnumber honeydew-collectors,
so ants are generally good for the home garden.
Spiders
Spiders generally evoke negative emotions in people, but you should truly be grateful for their
presence in your garden. The pest control service that spiders provide is enormous and greatly underappreciated. There are more than 800 species of spiders in Washington State, and the average
pesticide-free garden is likely to be home to 20 to 25 species.
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Spiders occupy a range of habitat niches with correspondingly different behaviors and prey
preferences. There are three main groups of spiders: those that spin and sit in webs to catch their prey;
those that are very active, foraging for prey, and often running it down; and those that sit still and
“ambush” prey when it comes too close. Garden web builders are perhaps the least threatening to
people because they are fixed in a location and not likely to surprise anybody (except for the
unfortunate winged insects that get caught in the web). Most often seen in late summer and autumn,
orb-weaving or “garden” spiders, spin their prominent, and sometimes large, webs in bushes and on
buildings, fences, and the like, catching and feeding on any winged insect that gets trapped.
Hunting spiders patrol backyards constantly searching for prey. Some species specialize on
ground-living prey, others roam over plants and trees, while others prefer to hunt on structures like
fences and buildings. Jumping spiders (salticids) are small to medium–sized spiders (1/4 to 1/2 inch
long) that jump and pounce on their prey. They are commonly found in Pacific Northwest gardens. All
hunting spiders devour a great number of insects every day.
Ambush spiders are masters of disguise, quietly waiting for prey to come to them. Crab
spiders (1/4 to 1/2 inch long) often wait in blooming flowers for insects seeking nectar or pollen. Some
sit on leaves waiting for an insect to land. Invariably, crab spiders are identically colored to their
background, and some can even change color to match the background they are residing on. By
spending a little time watching spiders in your garden, your negative feelings towards them may just
become positive!
Harvestmen
Closely related to spiders, harvestmen (known as daddy-long-legs) are common in gardens.
While the insect’s body may only measure 1/4 inch, its legs may stretch from 1 to 1½ inches long. The
story that harvestmen are the most venomous animals in the world is a myth—they contain no venom
and they are unable to puncture human skin. Most species are omnivores feeding on small insects and
mites, as well as plants, fungi, and dead organisms. Although they don’t control pests as well as
spiders and mites, they do play a small role in pest control in gardens.
Other species of encyrtids attack beetles, flies, caterpillars, grasshoppers, true bugs, and other
wasps. With more than 300 species of encyrtid wasps found in the United States, every garden likely
harbors some populations of these ubiquitous pest control agents.
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STRATEGIES FOR ATTRACTING AND KEEPING BENEFICIAL INSECTS IN YOUR
BACKYARD
The single greatest impediment to attracting and maintaining a good population of beneficial
insects and other arthropods in your backyard, is the regular use of synthetic, broad-spectrum
pesticides. Infrequent use of certain narrow-spectrum pesticides is more compatible with some
beneficial insects, but, generally, the fewer chemical inputs there are, the greater and more diverse the
beneficial insect community will be. Some native bees and butterflies are extremely sensitive to
pesticides, whether broad- or narrow-spectrum. Extensive lawns are also non-conducive to attracting
and retaining a diversity of beneficial insects, mites, and spiders, so it’s best to minimize lawn areas
and maximize shrub and bush plantings.
Populations of all the beneficial insects described in this publication reside naturally in
riparian (river- or creek-side) and other natural areas near many backyards. Natural dispersion from
these refuges ensures that some beneficial insects will visit backyards, but they will not stay unless
food, hosts, and shelter resources are available in the back yards. Native plants have closer affinities
with native insects, and therefore provide most of these resources. Current research at Washington
State University is identifying the plant species and communities that provide optimal resources for
beneficial insects and other arthropods (http://www.wavineyardbeautywithbenefits.com/).
Generally though, providing some elements of a native habitat in and around backyards, will
improve the abundance and diversity of natural enemies of pests and pollinators. A garden with a good
diversity of local, native flora will soon attract a good diversity of local, beneficial arthropods. Native
flora also provide natural overwintering sites for many beneficial insects, and it is useful to leave at
least a small area of native vegetation undisturbed during fall and winter.
Some species of beneficial insects (lady beetles, lacewings, predatory mites) are available for
purchase from commercial suppliers. However, the benefits from introducing these beneficial insects
to your garden are usually limited and short-lived. Upon release, commercially obtained lady beetles
and lacewings ten disperse and rapidly leave your backyard, despite the presence of prey and suitable
nectar resources. Purchased insects generally originate from non-local populations and may not be
well-adapted to the conditions of the Pacific Northwest.
Generally, it is more effective and sustainable to create a garden habitat that will be colonized
naturally. Food resources like sugar or yeast sprays are also commercially available and claim to
encourage beneficial insect residence in backyards. However, if there is already a diversity of
flowering plants available, these supplemental sprays are unlikely to significantly enhance populations.
Beneficial insect attractants based on volatiles (usually methyl salicylate) produced by plants when
attacked by pest insects, do have potential for attracting and retaining beneficial insects in the garden.
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These volatiles mimic the “distress signals” emitted by plants, and are therefore a reliable guide for
predators and parasitoids searching for food or hosts (http://www.agbio-inc.com/predalure.html).
By being a good host to beneficial insects, spiders, and mites, your diversified, native plantbased garden should rarely experience plant pest outbreaks. As a fully-functioning ecosystem, with a
diverse and balanced biological community, it will be as attractive, as it is practical.
Use pesticides with care. Apply them only to plants, animals, or sites as listed on the label.
When mixing and applying pesticides, follow all label precautions to protect yourself and others
around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or
clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and
keep them out of the reach of children, pets, and livestock.
RICE WEED MANAGEMENT IN THE PHILIPPINES
In the Philippines, many farmers rely on herbicides to control weeds in their rice fields,
particularly for direct-seeded (as opposed to transplanted) crops, as broadcast seed does not grow in
consistent rows, making manual weeding less efficient. Manual weeding and flooding are traditionally
used to restrict weed competition with crops, but their cost is rising due to increased labor and water
resource costs. Herbicides are easy to use, can achieve high rates of control with effective application,
and are, in many situations, relatively cheap, compared to manual or mechanical weeding. Indeed,
Rice farmers have generally been encouraged by the Philippine Rice Research Institute
(PhilRice) to use integrated weed management (IWM) strategies. This encouragement is primarily
aimed at maintaining crop yields, while reducing chemical use. IWM involves the use of a diversity of
weed control methods, including non-chemical strategies (such as full cultivation prior to
establishment). IWM can benefit the control of rice weeds by delaying the development of resistance
and/or allowing the control of herbicide-resistant weeds. The adoption of weed management strategies
that increase production and profit without depreciating future productive capacity, such as through
resistance development, will be higher where practices build on traditional methods and are
compatible with existing practices. This is particularly important given the significance of rice to the
Philippines and the increasing scarcity of key resources required for traditional farming systems, such
as labor and water. A statistical analysis that identifies the impact of various economic and noneconomic factors on the adoption and intensity of use of weed management strategies can thus provide
valuable input into the formulation of policies to promote sustainable agricultural production.
This involves the identification of those factors influencing the adoption and intensity of
herbicide use in rice fields. A random-effects double-hurdle model is applied to survey data that
collates responses from thousands of producers throughout the Philippines.
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PLAN CROPPING SYSTEMS TO MINIMIZE OPEN NICHES FOR WEEDS
The effect of weed on yield of rice Weeds are at present the major biotic constraint to
increased rice production worldwide. Unchecked weed growth caused 53% reduction in grain yield in
puddled conditions, and 91% yield reduction in non-puddled conditions (Ali & Sankaran, 1984). In
lowland or puddled conditions, broad-leafed weed are the main problem. Maximum grain yield (64
q/ha) was obtained in weed-free plots and minimum (35 q/ha) in weedy plots. The first weeding
operation is done 3-4 weeks after transplanting and need 25-34 labors/ha depending on the weed
density. The second weeding is generally done 15-30 days after first weeding and usually required 1215 labors/ha.
The hand removal of early emerged grassy weeds and sedges along with the broad leaved
species allowed lower accumulation of dry matter and these resulted in better crop growth which in
turn smothered the weed growth in comparison to others treatment. Hand weeding is generally not a
very efficient method. Probably 10-20% or more of the plants with 10 cm or more growth is left in the
field after weeding. On an average the efficiency of this method is not more than 70%.
Pyrazosulfuron ethyl is a new highly active sulfonylurea herbicide that has been widely used
for weed control in a variety of crops and vegetables. The sulfonylurea herbicides are highly active
herbicides that have been in commercial use since 1982. The mode of action of the sulfonylurea
(Chaleff, 1984; LaRossa, 1984) herbicides is the inhibition of acetolactate synthase (ALS). ALS a key
enzyme required in the biosynthesis of essential amino acids, valine and isoleucine, in plants. This
results in rapid inhibition of plant cell division and growth, although the symptoms of drying weeds
may not appear till 7-20 days after application.
The combination of herbicides and manual weed control has significant effect on controlling
weed of rice field. are the most costly category of agricultural pests, causing more yield losses and
added labor costs than either insect pests or crop disease. Because organic farming excludes the use of
synthetic herbicides, most organic farmers consider effective organic weed control a top research
priority. In particular, weeds are a constant fact of life in annual row crops, vegetables, and other
horticultural crops. With a little diligence, home gardeners can turn their weeds into beneficial organic
matter. However, weed control costs really add up in a one-acre market garden, and a weedy
vegetable field at the 10-100 acre scale can spell a crop failure.
Yet, if it weren’t for weeds, the world would have lost more topsoil than it has to date, and
humankind might have suffered mass starvation by now. Because weeds are pioneer plants that do a
vital job: they protect and restore soil that has been left exposed by natural or human-caused
disturbance. Watch any recently burned or logged forest area, and you will see precious topsoil
washing away in each heavy rain – until the brambles, greenbrier, pokeweed, poison ivy and other
brushy weeds cover the ground with their impenetrable tangle. These pioneer plants initiate the
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process of ecological succession that, if left uninterrupted, will eventually restore the climax forest or
other plant community native to the region.
In agriculture and horticulture, humans replace the native climax vegetation with a suite of
domesticated plant species chosen for their value as food, forage, fiber, or fuel, or for aesthetic
purposes. Annual crop production entails regular soil disturbance or clearing by tillage cultivation
and/or herbicides, which elicits a “weed response” from nature. Agricultural fields present different
environments from those left by a natural disaster or a forest clear cut, one characterized by repeated
soil exposure and relatively high levels of available nitrogen (N), phosphorus (P), potassium (K), and
other essential plant nutrients. Agricultural weeds are those pioneer plant species that can emerge
rapidly, exploit the readily available nutrients, and complete their life cycle before the next tillage or
herbicide application terminates their growth.
Weeds are a normal and natural occurrence in vegetables and other annual cropping systems.
Serious weed problems develop when a susceptible crop, a large weed seed bank in the soil (including
both true seeds and vegetative propagules of perennial weeds), and a favorable environment for weed
growth occur together.
Our most troublesome annual weeds reproduce through prolific seed production, and their
seeds often germinate in response to cues that competing vegetation has been removed. These cues
include light (exposure to a brief flash of daylight during tillage is sufficient), increased fluctuations in
soil temperature and moisture, improved aeration, or accelerated release of soluble N and other
nutrients. These weeds are most prevalent in frequently-tilled fields, but some can also thrive in annual
cropping systems managed no-till. Examples include common lambsquarters, pigweeds, galinsoga,
common purslane, velvetleaf, morning glories, foxtails, and crabgrass.
Our most troublesome perennial weeds are those that can regenerate new plants from small
fragments of root, rhizome, stolon or other underground structures. These weeds may or may not also
reproduce by seed. They plague both annual and perennial crops, and tend to increase when tillage is
reduced or eliminated. Examples include purple and yellow nutsedges, bermudagrass (wiregrass),
quackgrass, johnsongrass, Canada thistle, milkweeds, and field and hedge bindweeds.
Successful organic weed control – managing the land’s natural “weed response” to
cultivation – begins with an ecological understanding of weeds and their roles in the farm or garden
ecosystem. Whereas annual crops and weeds have similar growth requirements – ample NPK, full sun,
prepared seedbed, etc. – subtle differences exist that can be exploited to the crop’s advantage. For
example, the emerging seedling of a small-seeded weed like galinsoga or pigweed requires available
nutrients from the soil almost immediately to survive and grow. In contrast, an emerging corn, bean, or
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rye seedling can draw nutrients from reserves in its large seed for a couple of weeks before it becomes
dependent on soil nutrients.
Furthermore, some weeds, such as lambsquarters, common ragweed, and foxtails, respond
dramatically to high levels of soluble N, and their growth rate continues to increase with fertilizer
application rates well beyond the point at which corn – one of the heaviest-feeding crops – levels off.
Thus, farmers can avoid overstimulating weeds by using slow-release sources of N and other nutrients,
applied at rates sufficient to meet crop needs but no more.
In practice, any vegetation that comes up in a field or garden that the grower did not plant is
often collectively called “weeds,” regardless of whether it is causing problems. Trying to eradicate all
volunteer vegetation is hard on farm budgets, gardeners’ backs, soils, agro-ecosystems, fuel supplies,
and the wider environment. Managing a weed to protect crops usually does not require exterminating
the weed altogether.
A weed is any plant not intentionally sown or propagated by the grower that requires
management to prevent it from interfering with crop or livestock production. Sustainable weed
management recognizes the ecological role of weeds as well as their pest potential. Some innovative
farmers utilize certain weeds as nutritious food or fodder, habitat for natural enemies of insect pests, or
cover crops.
The goal of sustainable organic weed management is to minimize the adverse impacts of
weeds on crops, and sometimes to reap the benefits of weeds. Weeds are nature’s way of covering soil
that has become exposed by fire, flood, landslide, windstorms, clear-cutting, clean tillage, herbicides,
overgrazing, or other disturbance. Bare soil is hungry and at risk. The soil life, so vital to soil fertility,
goes hungry because the normal influx of nourishing organic compounds from living plant roots has
been cut off for the time being. The exposed soil surface is at risk of erosion by rain or wind,
especially if root systems have also been removed or disrupted. Pioneer plants – weeds – are those
species that can rapidly cover bare soil and begin performing a number of vital ecological functions:
•
Protect the soil from erosion.
•
Replenish organic matter, feed and restore soil life.
•
Absorb, conserve, and recycle soluble nutrients that would otherwise leach away.
•
Absorb carbon dioxide from the atmosphere.
•
Restore biodiversity.
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•
Provide habitat for insects and animals.
At the same time, agricultural weeds hurt crop yields or increase costs of production by:
•
Competing for light, nutrients, moisture, and space.
•
Releasing natural substances that inhibit crop growth (allelopathy).
•
Physically hindering or smothering crop growth (e.g., morning glories and bindweeds).
•
Hosting pests or pathogens that may attack crops.
•
Promoting disease by restricting air circulation around the crop.
•
Interfering with or contaminating crop harvest.
•
Reproducing prolifically, resulting in a greater weed problem next year.
•
Parasitizing crops directly (e.g., dodder, witchweed).
Annual vegetable and row cropping creates empty ecological niches – bare, unoccupied soil
with unutilized moisture and nutrients – for part of each season. Open niches may occur in time,
between harvest of one crop and establishment of the next; and in space, between rows until the crop
canopy has closed. Weeds emerge, grow, and reproduce in these open niches – until they are stopped
by cultivation, pulling, mowing, herbicides, or direct competition from crops.
One key sustainable strategy for dealing with weeds is to minimize open niches for weeds in
cropping systems, while maintaining satisfactory crop yields. In annual cropping systems and lesscompetitive perennials like asparagus and cut flowers, some open niches are unavoidable, whereas
others can be eliminated through cover cropping, tighter crop rotations, closer row spacing, and inter
cropping. Well-managed pasture, forage, orchard, permaculture, and agroforestry systems are
generally more “closed,” and usually require less intensive weed control efforts.
Plant species that have been introduced into our region from abroad often become serious
weeds, spreading unchecked in the absence of their natural enemies. Unlike most pioneer plants that
promote ecological succession back to native forest or prairie after a disturbance, some introduced
species, known as “invasive exotic plants,” actively smother or supplant native vegetation. Kudzu –
those enormous vines that cover and kill large trees – is perhaps the most dramatic example in our
region. A recent study has shown that kudzu does its damage, not just by shading, but also through a
powerful allelopathic effect. That is why no winter-hardy grasses, forbs, or wildflowers ever emerge
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through the tangle of dead kudzu vines in early spring. Ailanthus (“tree of heaven”) also supplants
native forest trees by allelopathy as well as aggressive growth. A small (1 – 3 ft) herbaceous invader
called garlic mustard has been shown to hurt forest trees by killing off their vital mycorrhizal fungal
symbiosis.
Some of the South’s worst agricultural weeds have also been introduced from abroad. Purple
nutsedge, native to the Old World tropics, is a small (4-24 inches) perennial sedge that can stunt
sugarcane and coffee trees through intense competition and allelopathy. It causes substantial crop
losses in the Deep South. Other exotic weeds include common bermudagrass, barnyardgrass, tropical
soda apple, crabgrass, Johnsongrass, and jungle rice. Two recent invaders of concern in the South are
Benghal dayflower and deep-rooted sedge.
Nationwide or regional coordinated eradication efforts are often directed at invasive exotic
plants. Musk thistle, spotted knapweed and purple loosestrife are three invasive exotics in the upper
South that have been successfully managed through classical biological control, the introduction of
specific insects that feed on those weeds in their areas of origin.
Because organic farmers do not use synthetic herbicides, they rely more heavily than
conventional growers on tillage and cultivation for weed control, especially in annual vegetable crops.
Unfortunately, while cultivation takes out existing weeds, it also stimulates additional weed seeds to
germinate. This can lead to a “cultivation treadmill” with which many vegetable growers are all too
familiar.
Furthermore, organic farmers seek to maintain a healthy, living soil rich in organic matter with
good physical structure (tilth). Frequent tillage and cultivation can burn up soil organic matter,
degrade soil structure, disrupt beneficial soil organisms like earthworms and mycorrhizal fungi, and
leave the soil more prone to erosion, compaction, and crusting. This creates a dilemma for organic
growers:
The answer is that ecological weed management combines planning and prevention with
control. Cultural practices such as crop rotation, cover cropping, mulching, and maintaining optimum
growing conditions for crops lessen weed pressure on the crop. These practices also help build soil
quality, and reduce the intensity and frequency of cultivation needed to accomplish adequate weed
control.
Controlling weeds in annual cropping systems without herbicides almost always entails some
tillage and cultivation. However, organic weed control does not simply substitute steel for herbicides.
Experienced growers develop site-specific systems for their farms, selecting materials and tactics from
a large weed-management toolbox (see sidebar), which continues to expand with ongoing research and
experimentation by farmers and scientists.
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Plan the crop rotation to keep the soil covered with desired vegetation or mulch as much of the
season as possible. Schedule plantings of each cash or cover crop as soon as practical after the
preceding crop is finished. When the vegetable is harvested, the cover crop is already established and
rapidly covers the ground. This minimizes the bare soil period at the vegetable. Different cover crops
may be better adapted to the warmer climates in the South, and our longer growing season may expand
opportunities for cover crop overseeding at different seasons.
No-till planting of vegetables or row crops into mowed, rolled, roll-crimped, undercut, or
winterkilled cover crops eliminates the bare soil period at the cover crop vegetable transition.
Whereas continuous no-till is not currently feasible in organic crop production, tillage can be reduced,
thereby minimizing soil degradation and flushes of weed germination. The no-till cover crop strategy
works best when weed populations are moderate, and the primary weeds are annuals, especially smallseeded annual broad leaf weeds, which are readily blocked by the mulch.
Summer Annual Weeds, such as pigweeds, smartweeds, common cocklebur, morning glories,
sicklepod, crabgrasses, foxtails and goosegrass, grow rapidly during the frost-free season, reproduce
through prolific seed production (thousands to hundreds of thousands per plant), and usually die with
the first fall frost. Their seeds often come up in “flushes” after tillage or cultivation. Management
tactics include timely shallow cultivation (the shallower the disturbance, the fewer additional seeds are
stimulated to germinate), mulching (most effective for small seeded broad leaf weeds), and rouging
out late-season “escapes” to interdict seed formation. Rotating to summer cover crops and coolseason vegetables can disrupt their lifecycles and thereby reduce weed pressure.
Winter Annual Weeds, such as common chickweed, deadnettles, shepherd’s purse, wild
mustards and annual sowthistle, also reproduce prolifically by seed, and emerge in response to tillage
or light stimulus. They are winter hardy, emerge in early fall or early spring, flower and set seed in
late spring, and die back in summer. They are troublesome for garlic, salad greens, and other cool
season vegetables, and can host pathogens and insect vectors of summer vegetables, such as tomato
spotted wilt virus carried by thrips. Timely shallow cultivation, winter cover crops, and rotating to
late-planted summer vegetables help keep winter annual weeds in check.
Simple or “Stationary” Perennial Weeds, such as dandelion, broad leaf dock, pokeweed, and
tall fescue, arise each year from winter hardy taproots, root crowns, or sturdy fibrous root masses.
They reproduce mainly by seed, and newly emerging seedlings can be controlled by timely shallow
cultivation. These weeds are more troublesome in pasture and perennial crops than in annual crops.
Light or local infestations can be dug out. Repeated close mowing can slowly weaken rootstocks, and
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vigorous tillage alternating with heavy smothering cover crops can reduce more widespread
infestations.
Biennial Weeds, such as burdock, prickly lettuce and wild carrot share characteristics of both
winter annual and simple perennial weeds.
They come up during spring through late summer,
overwinter as rootstocks, then emerge, bolt, and set seed the next spring.
Timely mowing,
undercutting, or digging just before flowering can interrupt propagation.
Invasive or “Wandering” Perennial Weeds, such as quackgrass, bermudagrass, johnsongrass,
nutsedges, Canada thistle, and bindweeds, are generally the most serious.
They form extensive
underground perennial structures – roots, rhizomes, bulbs, or tubers – from which they propagate and
spread, often over a wide area. Many of these weeds can regenerate from a one-inch fragment of
rhizome buried several inches deep in the soil. Thus, a single disking or rotary tillage that chops up the
rhizomes will propagate the weed. However, repeated tillage whenever regrowth reaches the 3–4 leaf
stage can weaken these stubborn weeds. Competitive cover crops such as buckwheat, sorghumsudangrass, or winter rye planted after tillage will counteract the damaging effects of the soil
disturbance and help suppress weed regrowth. Mowing every four weeks to a short stubble height can
slowly weaken invasive perennials, and may be the best option in pastures other non-tilled situations.
Strategies to reduce weed niches in space (between crop rows) include inter cropping
(companion planting), relay cropping (including cover crop overseeding), alley cropping, agroferstry
systems, strip tillage, and living mulches.
NEEM
Medicinal properties of the Neem tree, botanically known as Azadiracta Indica, were first
recognized in Indian subcontinent thousands of years ago, when founders of Ayurveda attributed
healing properties to every part of the tree. Sanskrit scholars dubbed it ‘Sarva Roga Nivarini’ which
translates as the curer of ailments. The Neem leaf, bark and roots are seen to contain alkaloids and
liminoids, of great medicinal value. Recent research has only confirmed this information.
Neem’s benefits as an air purifier was known long back. It was no co-incidence that Emperor Ashoka,
in the 3rd century before Christ, commanded that Neem be planted along the royal highway and roads
along with other perennials like Tamarindus indica and Madhuca Latifolia (Brahmachari, G., 2004)
It is not for nothing that the Neem tree in the South Asian culture has been ranked higher than
‘kalpavriksha’ the mythological wish–fulfilling tree. In ‘Sharh-e- Mufridat Al-Qanoon’, Neem has
been named as ‘Shajar-e-Mubarak’, ‘the blessed tree’, because of its highly beneficial properties.
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Thus a small Neem seed planted by an individual today will continue to purify the air of pollutants and
noxious elements for the next 450 years and more. It will also improve the fertility of the soil for the
next four centuries and more.
The Neem tree is globally being acknowledged as the most valuable tree in the world, in terms
of health, commercial and industrial potential. The WHO has named it “The Tree of the Century”.
Neem is the grand old tree of the Bangladesh countryside. It has for centuries been the cornerstone of
Bangladeshis health traditions. A Neem-rich nation would translate into a healthy and wealthy next
generation. It would also make for a cleaner, greener and more fertile Bangladesh.
PERMACULTURE, CROPS AND WEEDS
Permaculture is a system for designing highly diverse communities of food producing and
other useful plants that leave little room for unwanted plants. Permaculture begins with a careful
analysis of the site, on which a site-specific design is based. Most permaculture designs emphasize the
use of perennial plant species and limits tillage for annual crops to a minor percentage of the landscape.
Similarly, some indigenous cultures in Mexico and other developing countries maintain multi-tier food
gardens with tree, shrub, and annual herb canopies containing as many as 75 useful plant species
growing together, including a few that US farmers might consider weeds.
Organic mulches such as straw, old hay (preferably seed-free), or chipped brush restrict niches
for weed growth by blocking light stimuli and offering physical hindrance to emerging weed seedlings.
These mulches are most effective against annual weeds. Black plastic mulch or landscape fabric (weed
barrier) can block out many perennial weeds, although some weeds emerge through planting holes,
and nutsedges and a few other weeds can penetrate the mulch itself.
With the exception of the synthetic mulches, all of these strategies to minimize weed niches
also add organic matter, build soil quality, and/or enhance farm biodiversity. Gardeners and growers
with limited land area usually implement bio-intensive methods to close off weed niches in their crop
rotations.
Vegetables are spaced close together for rapid canopy closure, cover crops are used
intensively and cut to generate mulch or composting materials, and each crop is planted immediately
after the preceding crop is harvested.
Some farmers with more land area alternate several years in cultivated annual vegetable crops
with several years in a perennial grass-legume sod, often managed as pasture or hay land. These
rotations help limit the buildup of annual weeds such as pigweed, lambsquarters, galinsoga, crabgrass,
and foxtails.
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Their motto is weed the soil, not the crop. In each rotation block, they grow only one
production crop every two years. The rest of the rotation schedule consists of high-biomass cover
crops, and a short (six week) fallow period during the summer of the non-production year. Frequent,
shallow tillage during the fallow period draws down the weed seed bank, while the heavy cover crops
on either side of the fallow choke out emerging perennial and annual weeds, and provide plenty of
organic matter to compensate for the six weeks of soil disturbance.
Once a crop rotation has been planned that minimizes opportunities for weed growth, the next
step is to design the system to facilitate weed control throughout the season. Develop control strategies
to address anticipated weeds in each major crop, and select tools for pre-plant, between-row, and
within-row weed removal. Plan bed layout, row spacing, and plant spacing to facilitate precision
cultivation. Choose irrigation methods and other cultural practices that are compatible with planned
weed control operations.
Because row spacings may vary from four inches to six feet in a diversified rotation, matching
cultivation tools and row spacing can be challenging. Use row spacings that are multiples of one
another and are compatible with equipment dimensions to facilitate mechanized cultivation.
Cultivation is done with two toolbars. The first carries four sweeps set to run between rows
and in the alleys behind the tractor tires. The second carries three sweeps that can be raised to leave
crop rows untouched, or lowered to cultivated unoccupied rows in one-row and two-row plantings. In
this and other systems, precise spacing of crop rows and of cultivation equipment is essential to
optimize weed control and avoid crop damage. Both mechanical and computer-based optical guidance
systems have been developed to keep tractor-drawn cultivation implements “on course” with respect to
the crop.
Farmers, researchers, and agricultural engineers have developed a wide range of tools for
precision cultivation, flame weeding, and other weed control operations in many different vegetable
and row crops. The toughest weeds to manage are those within the crop row. The simplest approach,
effective on small weeds (less than one inch) in established crops (6–18 inches tall) is to adjust shovel,
sweep, or rolling cultivators to throw just enough soil into the row to bury and smother the weeds.
Several within-row implements, including finger weeders, torsion weeders, tine weeders, and
“spyders” have been designed to uproot or sever weeds seedlings while leaving larger crop plants
intact. Computer guided weeders have been designed to recognize the crop and move out of the row,
then back in to get between-plant weeds. These implements are not as dependent on the crop-weed
size differential. They cost $30,000 or more, yet can pay for themselves in time saved within a year or
two on a mid-scale vegetable farm.
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Most cultivation implements work best in soils with good crumb structure (tilth), and become
less effective in killing weeds if the soil is cloddy, crusted, or compacted. Wet soil will clog many
implements. Brush hoes may be a good choice for frequently wet fields. In stony soils, sturdy
implements, and implements equipped with spring mechanisms, such as a springtooth harrow,
function best, and are least likely to become damaged by impacts with stones.
For homestead and market gardens managed with hand tools, a great diversity of hoes and
weeders have been developed for every need, ranging from light weight collinear hoes and trapezoid
hoes to take small weeds out of young crops, to oscillating (stirrup) hoes, and heavy-duty standard
hoes suitable for larger weeds. Earth Tools, Inc (see Resources) is an excellent source for high quality
hand tools.
Before investing in new equipment, evaluate tools and other resources already on hand to
determine what additional weed control implements are needed. Consider crops being grown, cultural
methods, main weeds and when they become problematic, soil conditions, climate, farm scale, and
budget.
For example, suppose edamame soybean is a major crop on a 20-acre vegetable farm, and
summer annuals dominate the weed flora. The farmer has found that removing weeds from within crop
rows improves yield, but hand weeding is impractical at this scale, and within-row weeds can get too
large for the farm’s torsion weeder if cultivation is delayed a few days. Soybean is a crop that can be
blind cultivated with a rotary hoe just before emergence, a practice that increases the crop–weed size
differential, and thereby widens the time window for effective use of the torsion weeder. Thus, a rotary
hoe may be a wise investment for this farm.
Other crops such as sweet corn, Irish potato, and broccoli tolerate and even benefit from
hilling-up once they are established. For these crops, a simple, inexpensive between-row cultivation
system with sweeps or rolling cultivators can be adjusted to throw soil into crop rows. The implement
simultaneously severs between-row weeds and buries weeds within and near the row.
A flame weeder can be a good investment for crops such as corn that can tolerate a brief blast
of heat at certain stages of development. Also, flame weeding just before emergence of small-seeded,
slow-germinating crops like carrot, parsley, and beet can wipe out emerging weed seedlings, and
thereby allow the crop to emerge in a clean seedbed.
Multi-acre organic production of weed-sensitive crops like carrot and onion may require
sophisticated strategies.
Researchers working with organic carrot farmers in Italy developed an
integrated weed control system that yielded substantial net savings in labor costs.The growers’
standard production system was to seed carrots in five 3-inch-wide bands spaced 12 inches apart
(center to center) on a 6-foot wide bed, flame-weed pre-emergence, tractor-cultivate between crop
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bands, and hand-weed within bands. The experimental strategy changed the planting pattern to ten
rows spaced 7 inches apart, and utilized an innovative precision cultivating machine that combined
3.5-inch between-row sweeps with vibrating tines and torsion weeders for weeds near and within crop
rows. This system reduced total weed control labor costs and often enhanced carrot yield.
Many organic farmers use black polyethylene film (black plastic) mulch as their main weed
management tool in tomato, pepper, melon, and other high value crops. Black plastic can block
emergence of many grass and perennial weeds that can penetrate organic mulch, and its soil-warming
effect is especially advantageous when an early harvest is desired.
Plastic does not add organic matter to the soil, and must be removed at the end of the season
and hauled to a landfill, labor and environmental costs that should be taken into account.
Biodegradable plastic mulches have been developed that give good weed control and do not require
disposal; however these are not currently allowed in certified organic production.
In a plastic-mulched crop, weeds emerging through planting holes need to be pulled. Alleys
between plastic-covered beds also require cultivation or other weed control measures. A few weeds,
notably nutsedges, can puncture and grow through plastic mulch. Black plastic can even accelerate the
spread of purple nutsedge by warming the soil. Vining weeds like morning glories and bindweeds
grow toward planting holes and climb the crop. Despite these limitations, many growers consider
plastic mulch highly cost-effective.
Organic mulches such as hay or straw can be effective against annual weeds in tomato and
many other vegetables. They are often used to control weeds down alleys between plastic-mulched
beds. Organic mulch cuts off weed seed germination stimuli, hinders weed emergence, conserves soil
moisture, adds organic matter and nutrients, and harbors some beneficial organisms. However, hay
mulch can itself be a source of weed seeds or damaging herbicide residues (see sidebar), so check your
sources!
Because spreading organic mulch by hand becomes costly at the multiacre scale, some
growers invest in a bale chopper to mechanize application of small rectangular bales. Others use a
flail mower and forage wagon to harvest, transport, and unload mulch grown on-farm; or a crimproller to convert cover crops into an in situ mulch. However, perennial weeds can readily penetrate
organic mulches or rolled cover crops, so get the perennial weeds well under control before investing
in capital equipment for organic mulching systems.
Several pyridine carboxylic acid herbicides commonly used to control pasture weeds can
persist for up to three years, leading to severe damage in tomato, squash, and other vegetables
mulched with hay harvested from treated fields. These include clopyralid (product trade names
include Curtail, Scorpion, Reclaim, Confront, Stinger, and Accent Gold); picloram (Grazon, Torden),
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and aminopyralid (Milestone, Forefront), and a newly released pyrimidine carboxylic acid,
aminocyclopyrachlor. Another related herbicide, triclopyr (Crossbow, Garlan, Remedy), can persist
for 3-12 months.
Each weed species is adapted to the patterns of soil disturbance, other stresses, and available
resources that characterize the particular crops or farming systems in which that weed thrives. This
pattern – or weed niche – is shaped by: crops grown; seasonal timing of tillage, planting, cultivation,
mowing, and harvest; methods and depth of tillage and cultivation; timing, types, and amounts of
fertilizers; irrigation method and schedule; climate; soil type and soil conditions. When the same
crops are planted and the same practices are used year after year, the populations of certain weeds can
explode. Conversely, a complex crop rotation that varies timing of field operations as well as plant
family creates a more changeable environment that can “keep the weeds guessing.”
For example, continuous corn or a simple corn-soy rotation, in which fields are moldboardplowed every spring before planting, is known to promote velvetleaf, cocklebur, and other aggressive,
large-seeded summer annual weeds that can emerge from several inches depth. In addition, certain
weeds can proliferate in more diverse rotations if the soil is tilled on a predictable schedule each year.
Vegetable farmers who rototill before each crop to prepare the seedbed are often plagued by heavy
populations of small seeded annual weeds like pigweeds, lambsquarters, galinsoga, purslane, and
foxtails. A four-year rotation of sweet corn, snap beans, cucurbit family, and tomato family, with
winter cover crops each year, can allow these weeds to build up, as they germinate in response to late
spring tillage ahead of vegetable planting. Adding cool season vegetables and competitive summer
cover crops to the rotation shifts timing of field operations, and can slow the buildup of these weeds.
Rotating fields into perennial cover for two or three years (e.g., orchardgrass + red clover) can
be especially effective in disrupting the life cycles of annual weeds. Perennial cover removes the
tillage stimulus for weed germination, and provides continuous habitat for ground beetles and other
consumers of weed seeds, thereby reducing weed populations.
Another strategy is to plant a field or bed in a succession of salad greens, radishes, and other
quick maturing crops for a year. Seedbed preparation for each crop knocks out weeds before they can
propagate, and can thereby draw down populations of weeds that become problematic in longer-season
vegetables like melon or tomato.
Crop diversity also impacts weeds directly. Various crops compete against weeds by rapidly
forming a dense, low canopy within crop rows (snap bean, Irish potato) or across the field (sweet
potato, cucurbits, cowpea); by growing tall (corn, tomato); by forming extensive root systems that
“grab” soil moisture and nutrients (sorghum-sudangrass); or not much at all (onion, carrot). Thus,
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common purslane might die out under a sweet potato canopy, grow slowly in established sweet corn
without affecting yield, and compete severely against summer-sown carrot.
Each plant species (crop, weed, or native plant) gives off a unique mixture of natural
substances that retard (or occasionally promote) the growth of certain other plant species. This
phenomenon is called allelopathy. In a diverse crop rotation, most weed species are exposed to
significant crop competition or allelopathy sometime during the rotation. Some tips for designing crop
rotations to keep weeds guessing include:
•
Vary timing of operations as well as plant family.
•
Include warm- and cool-season crops, and short- and long-season crops.
•
Vary depths and methods of tillage.
•
If weed pressure is moderate, include no tillage cover crop management at some points in the
rotation.
•
After several years in annual crops, rotate the field into perennial cover for 1-3 years.
Finally, remember that weeds are constantly adapting and responding to weed management
tactics, both at the species level (genetic changes), and at the community level (changes in weed flora).
As a result, using the same strategy year after year will eventually select for weeds that can thrive
despite the stresses imposed. For example, conventional agriculture is now plagued by herbicideresistant weeds. Weeds can also adapt to non-chemical tactics, so avoid relying on one weed control
tool, tactic, or strategy, no matter how successful it initially appears.
In organic weed management, crop vigor is the first line of defense against weeds. Whereas
timely cultivation knocks the weeds back, the most economical and soil-friendly way to keep crops
ahead of the weeds is to optimize the health and vigor of the crop itself. Vegetables that emerge,
establish, and grow rapidly get through their “critical weed-free period” early in the season. Crops that
quickly form a closed canopy (completely shading the field or bed) can hinder weed growth and
reproduction in a manner similar to cover crops.
The challenge for organic vegetable farmers is that most annual crops are vulnerable to weeds
early in the season when the crop is small. Some vegetables, such as carrot and onion, grow slowly
and may not fully occupy the space even at maturity. However, optimal crop management can make
any vegetable more weed-tolerant and weed-competitive.
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Following are several management practices that can enhance crop competitiveness toward
weeds:
•
Choose vigorous, locally-adapted crop varieties.
•
Use high-quality seed.
•
Grow and set out vigorous transplants when appropriate.
•
Maintain healthy, living soil.
•
Optimize crop nutrition.
•
Choose optimum planting dates whenever practical.
•
Adjust row and plant spacing to shade out weeds.
•
Maintain optimum crop growing conditions.
•
Feed and water the crop, not the weeds.
Crop varieties that are well suited to the farm’s climate, rainfall patterns, and soils will grow
more vigorously than varieties bred for warmer, cooler, wetter, drier or more fertile conditions. Find
out from neighboring farmers and local seed suppliers what varieties seem to work best in your locale.
Crop varieties vary in height, spread, and density of canopy. Tall or long-vine varieties with
dense foliage compete more effectively against weeds than shorter varieties with less foliage. Some
older, heirloom crop varieties compete better against weeds than modern varieties. For example, in
the southern Appalachian region, ‘Danvers’ carrot produces a large, dense top that shades out weeds
by the middle of its growth cycle, while ‘Nantes’ forms less top growth and requires more weeding,
and some modern, specialty cultivars like 'Minicor' and ‘Cosmic Purple’ have small, thin tops, and
must be weeded regularly until maturity. Recent studies have shown that pea and potato varieties with
heavier foliage compete better against weeds. Note that heavy canopy can be a disadvantage in
situations where fungal diseases pose a significant threat to the crop (e.g., Alternaria in carrot). Use
high quality seed that will germinate and grow rapidly. Discard old, slow-germinating, partially-viable
seed, unless you are salvaging a hard-to-replace heirloom variety or breeding line.
Transplanting gives vegetables a head start on weeds. Sow seeds in a good, weed-free
greenhouse mix to produce vigorous “starts.” Lettuce, tomato family, brassicas and onion family
transplant especially well. Some organic growers also transplant cucurbits, corn, pea, bean, and even
spinach, chard, beet, and turnip, in order to beat the weeds.
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Maintain a healthy, living soil to promote crop vigor. Fine-tune nutrient levels and soil
conditions to match the needs of each crop. For most vegetables, slow-release sources of nitrogen (N),
such as compost, residues of a grass + legume cover crop, or feather meal match crop needs best, and
are less likely to “over-amp” N-responsive weeds like lambsquarters, pigweeds, ragweed, and
quackgrass than faster-release N sources like blood meal or a succulent, all-legume green manure.
However, don’t hesitate to fertilize a “hungry” crop with the appropriate organic fertilizer, as an
underfertilized vegetable is vulnerable to weeds that tolerate lower fertility.
Plant each crop when temperatures and moisture levels are favorable to that crop, and are
likely to remain so until harvest Trying to stretch the season for a given crop by planting earlier or
later than usual can make the crop less vigorous and more prone to weeds. Utilize season extension
techniques to maintain more favorable conditions for the crop, and plan on a little extra labor for weed
management.
Temperatures above 95°F cause stress and reduce quality in most food crops, while certain
weeds, notably Palmer amaranth and purple nutsedge, attain their peak growth in such heat. When it
gets this hot, plant aggressive, heat-loving cover crops, and take a break! Many vegetable farmers in
Florida and across the Deep South suspend production during the heat of summer, and resume in the
fall (see sidebar).
In crops and locations where disease is not a concern, use plant and row spacings to promote
early canopy closure without overcrowding the crop. Some vegetables can be planted in double or
multiple rows on raised beds to speed canopy closure and facilitate between-bed cultivation. Use inrow drip irrigation or fertigation to water and feed the crop but not the weeds. Subsurface drip
irrigation (line installed several inches below the surface in crop row) is especially effective, providing
water to established crops while leaving near-surface weed seeds within the row dry and dormant.
Grow the least competitive vegetables (carrot, onion, etc.) on fields with a recent history of
low weed populations or effective weed control. Plant weedier fields to competitive crops like potato,
sweet potato, winter squash, and cowpea.
Milagro (“Mila”) Berhane, community gardener and Extension Specialist in Horticulture at
Southern University in Baton Rouge, LA, describes weeds as “a struggle and a significant barrier to
successful organic vegetable farming.” Her worst weeds include johnsongrass, bermudagrass, other
grasses, yellow nutsedge, and morning glories.
Mila grows two acres of variety trials (sweet corn, cowpea, cucumber) as well as a large
community garden. She manages weeds successfully through strategic crop timing, use of transplants,
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and cultivation with a wheel hoe equipped with stirrup hoe attachments. She avoids plastic mulch
because it is easily penetrated by the nutsedge, requires end-of-season pickup, and entails
environmental costs.
Mila has learned when different vegetables grow best in her part of Louisiana (hardiness zone
8b). Broccoli, collard, turnip, and other brassicas thrive when transplanted late in August so that they
grow as summer heat subsides. Carrot, beet, and spinach do not establish well when temperatures are
above 80°F, so she plants them in November or December.
Regarding warm-season vegetables like summer squash and snap bean, Mila notes that “the
weeds start in April and are worst in summer, so we start planting in March, and do our last spring
planting in May.” Tomato and pepper planting is delayed until August to avoid weed and disease
pressure. “Peppers do great in the fall, producing until December.”
When the soil begins to warm up in February, Mila tills and shapes beds by tractor, waits for
several weeks (stale seedbed), tills again, and immediately transplants spring crops to get the jump on
the April flush of weeds. Whenever a bed become vacant in late spring or summer, she tills, does
another stale seedbed, then plants cowpea to compete with the weeds. “I plant cow peas anytime the
soil is warm, from May on, sometimes to pick peas, and sometimes as a cover crop only.”
Additional strategies include straw mulch after last cultivation, in-row drip irrigation, and
manual removal of weeds to prevent seed set. She has reduced pigweed and curly dock populations to
non-troublesome levels, and is working on similarly reducing the morning glory seed bank. Her
experience shows that good Integrated Weed Management that includes a strategy of taking the
summer off, can give good weed control without herbicides, plastic, or an aching back, even in a hot,
moist climate with intense weed pressure.
Cover crops do the same job as weeds, only better. Cover crops are domesticated plant
species that grow vigorously with relatively little care, and are used to prevent soil erosion during
fallow periods. They perform many of the same ecosystem functions as weeds: cover and protect bare
soil, feed the soil life, conserve and recycle nutrients, enhance biodiversity, and harbor beneficial
insects. Cover crops suppress weeds in several ways. First, cover crops occupy the space and limit
weed growth through direct competition for light, nutrients, and moisture.
Second, many cover crops and their residues release allelochemicals into the soil that prevent
or hinder weed seedling growth. Winter rye, oats, barley, sorghum-sudangrass, buckwheat, forage
radish, subterranean clover, and sunflowers have been shown to exert allelopathic effects against
certain weeds.
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Third, a vigorous cover crop can change the environment for weed seeds on and in the soil.
Whereas a brief flash of unfiltered daylight stimulates weed seed germination, the dim green light
under a heavy crop canopy can actually inhibit germination. The canopy also reduces thermal stimuli
by lowering soil temperature and dampening daily fluctuations. Sometimes, weed seed germination
remains inhibited for a period of time after the cover crop is terminated, thereby reducing weed
populations in a subsequent vegetable crop.
Whenever a bed or field becomes vacant, put the weeds out of a job - plant a cover crop
immediately so that it can begin the vital restorative work that nature does with weeds. Innovative
farmers have developed many weed management strategies in which cover crops play a major role.
Whereas the long, hot growing seasons of the South promote rank weed growth, they also
expand opportunities for cover cropping.
Warm-season crops like forage soybean, sorghum-
sudangrass, and Japanese, pearl, and foxtail millets, choke out weeds, and produce tremendous
biomass within 50-70 days after planting. Buckwheat and cowpea form especially heavy, shading
canopies, and are excellent weed deterrents for short summer fallow periods.
During the cooler part of the year, cereal grains can be grown with hardy annual legumes. Bi
cultures generally give better weed suppression and soil building than either grain or legume alone.
Rye, wheat, hairy vetch, crimson clover, and Austrian winter pea can be grown over winter throughout
the South. Oats, barley, field pea, common vetch, bell bean, and berseem clover grow vigorously in
the milder winters of the Deep South. Daikon and forage radishes are especially weed-suppressive
and are frost hardy to about 20°F.
Cover crops will not solve all weed problems or eliminate the need for cultivation. Yet, cover
cropping is one of the more important "little hammers” of ecological weed management, as they can
reduce weed control costs and limit weed seed set while fields are not in production. In addition, cover
crops replenish organic matter, feed soil life, add nitrogen (legumes), make other nutrients more
available, prevent erosion, and providing habitat for natural enemies of insect pests. Take these
benefits into account when evaluating the economics of cover cropping as a weed management tool.
Use good planting technique, sufficiently high seeding rates, and high quality seed, in order to
obtain a dense, weed-suppressive cover crop. Don’t hesitate to water or feed a cover crop seeding
(compost, aged manure, or amendments based on a soil test) if needed to get it off to a good start.
One limitation of cover cropping can arise when the cover crop is incorporated into the soil as
a green manure. This tillage reopens the niche for weeds until the subsequent production crop becomes
established and occupies the soil. Decomposing cover crop residues can inhibit, not affect, or stimulate
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weeds, depending on cover crop species, biomass, and maturity, soil and weather conditions, and weed
species present in the field. As a result, green manures may or may not reduce weed pressure in a
subsequent cash crop.
Many annual cover crops can be killed by mowing or rolling after full bloom to create mulch
in place. This eliminates soil disturbance and bare soil periods between the cover crop and the next
cash crop. Whereas these “organic no-till systems” can be challenging to manage, an increasing
number of farmers have adopted them, especially for summer vegetables after winter cover crops.
BEATING THE WEEDS WITH INNOVATIVE COVER CULTIVATION
There is an innovative, integrated weed management strategy for vegetable farms. In addition
to winter cover crops of rye + vetch and oats + peas, it is possible to inter crop vegetables with other
widely-available, low-cost cover crops. Red clover is over seeded into winter squash. This hardy,
shade-tolerant clover gets established under the squash foliage, rapidly covers the ground after harvest,
and is allowed to grow through the following season to reduce annual weeds and rebuild the soil.
When it is time to roll out the steel, farmer combines the efficiency of mechanization with the
fine precision of the human eye and hand. Farmers designed tractor drawn platforms from which
workers can comfortably hand weed or operate tractor-mounted wiggle hoes while the tractor moves
slowly down the row. He also has a range of tractor drawn implements, from Buddingh basket
weeders for tiny weeds to more aggressive Lilliston rolling cultivators and Regi weeders for larger
weeds in established crops.
The reason so many weeds come up soon after tillage is that most soils have a large weed seed
bank – millions of viable, dormant weed seeds per acre, waiting for the right stimuli (such as the light
flash, improved aeration, or accelerated N mineralization associated with tillage; or the wider
temperature fluctuations under exposed soil) to germinate and emerge. The weed seed bank is the
reserve of viable weed seeds present in the soil, and consists of new weed seeds recently shed and
older seeds that have persisted from previous years. The weed seed bank also includes the tubers,
bulbs, rhizomes, and other vegetative structures through which invasive perennial weeds propagate.
Every year, weed seed germination, seed decay, and seed consumption by soil organisms draw
down the weed seed bank. Then, when the current season’s weeds shed their seeds, they replenish the
weed seed bank. Another source for the weed seed bank is the inadvertent arrival of new weed seeds
in organic amendments or crop seeds brought onto the farm, in soil carried on footwear or farm
equipment, or via wildlife, irrigation, or flood waters. These “seed imports” tend to be small in
numbers, but potentially serious if a new, aggressive weed species is introduced onto the farm.
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It is especially important for organic farmers to pay close attention to the weed seed bank.
Good organic weed management depends on effective measures to limit weed seed set, as herbicides
cannot be used to kill a heavy flush of weeds. Also, the efficacy of mechanical cultivation declines as
weed population density increases. A small percentage of weeds will escape even the best cultivation
tools, and a small percentage of a high weed population can still hurt yields.
Managing the weed seed bank entails encouraging “withdrawals” and minimizing “deposits.”
Seed inputs can be reduced by cutting or pulling weeds before they set seed, and by mowing or tilling
fields as soon as crop harvest is complete.
“Walking the field” to remove large weeds from
established crops before the weeds set seed is a good way to reduce seed bank deposits. Some growers
find that the added labor is a good investment, even on multi-acre fields. Note that large weeds in full
bloom can sometimes form mature seeds after being severed or uprooted; they should be chopped fine
(e.g., with flail mower), or removed from the field.
Competitive cash and cover crops can reduce weed seed deposits, since a small weed that
grows and matures in the shade of a crop may produce 100–10,000-fold fewer seed than a large weed
of the same species growing in full sun.
Good sanitation – measures to prevent the introduction of new weed species on the farm – can
go far toward preventing future weed problems. When using mulch hay from off farm sources, try to
get seed-free hay if possible. Compost manure at high temperatures (140°F for a week, turn to be sure
all parts of pile reach this temperature) before spreading. Remove soil from boots, tractor tires, tiller
tines, and other equipment before entering the field, especially if the soil comes from another farm.
Power-wash shared or rented equipment before and after use. Check crop seed sources to verify that
they are free of “noxious weed seeds.” Filter irrigation water before applying to fields, if it comes
from rivers that might transport weed seeds from upstream.
It can be virtually impossible to eliminate all off-farm sources of weed seeds. Wildlife, flood
waters and other factors beyond the farmer’s control can bring new weed species to the farm. Be
vigilant – regular field monitoring can detect a new infestation while it is still small and local enough
to eradicate.
On the other side of the ledger, try to make some hefty withdrawals from the weed seed bank.
One excellent technique is stale seedbed. Till the soil several inches deep several weeks before crop
planting, watch closely, and cultivate when a flush of weeds emerges. Cultivate again immediately
before planting, this time going very shallowly (0.5-1 inch) to avoid stimulating more weed seeds to
sprout with the crop. If the final flush of weeds is mainly broad leaf species, you can flame weed to
avoid further soil disturbance.
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Encourage weed seed predation. Ground beetles, crickets and some other ground-dwelling
insects eat weed seeds. Birds, some species of field mice (not the voles that damage crops) and even
slugs (which can damage crop seedlings) glean newly-shed weed seed from the ground. Research has
shown that weed seed predation can reduce the current season’s deposits by 50–90% (Menalled et al.,
2006). Mow fields promptly after harvest to stop further weed seed formation, but consider delaying
tillage to give the “cleanup crew” a few weeks to eat weed seeds already shed. Cover crops can
sometimes be inter seeded into production crops, or no-till drilled after harvest, to allow both weed
seed predation and prompt cover crop establishment.
Provide year round habitat for ground beetles and other weed seed predators by keeping at
least part of the field covered by living vegetation or organic mulches as much of the season as
possible. Reduce tillage if practical, in order to lessen disruption of habitat for weed seed consumers.
The “control” part of organic weed management aims to remove weeds that threaten current or
future production at the least possible cost in labor, fuel, machinery, and soil quality. Trying to
eliminate every weed on the farm would likely lead to red ink and defeat efforts to build healthy soil.
Thus, the farmer must continually evaluate when weed control operations are necessary or most
advantageous. Generally, the critical times for weed control are:
•
When the crop is planted.
•
When flushes of weed seedlings are just emerging.
•
During the crop’s minimum weed-free period.
•
When perennial weed reserves reach their minimum.
•
Before weeds form viable seed or vegetative propagules.
The weeds that do the most damage to crops are those that emerge before or with the crop.
Thus, is it vital to plant into a clean seedbed. A seedbed prepared several days before planting may
look clean, yet have millions of germinating weed seeds per acre, already getting a head start on the
crop to be planted. Whenever possible, plant immediately after the final step in preparing the soil –
whether that step is harrowing, rototilling, incorporating amendments, shaping the beds, or strip-tilling
the crop rows. When in doubt, lightly stir the soil surface with your fingertips or a rake and look for
the “white threads” of germinating weeds.
For many crops, blind cultivation can be used to keep the seedbed clean until the crop is up.
Larger-seeded vegetables can be rotary-hoed to give them a head start. Weed seedlings that emerge
ahead of slow-germinating crops like carrot can be flamed. Some farmers time this operation by
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covering a small patch with a pane of glass. When the crop first emerges under the glass, the field is
flame-weeded. The rest of the crop then emerges a day or two later, in a clean field.
Timely cultivation, flame weeding, mowing, manual pulling, or mulching can make the
difference between success and failure. Early in the season, when the crop is just getting established,
get the weeds while they are small. Cultivate shallowly when weeds are just emerging and in the
white thread stage. Timely shallow cultivation makes lighter work for the gardener, saves fuel for the
farmer, reduces soil disturbance, and destroys millions of weeds per acre before they cause trouble.
In flame weeding, the flamer should move over the ground at a speed and height that briefly
scalds emerged weeds, rather than charring them. Properly flamed weeds may take a few hours to
show visible signs of damage, then die overnight. Over flaming wastes fuel, and may damage soil life
or increase fire hazards. broad leaf weed seedlings with exposed growing points are most readily
killed by flaming. Grass weeds, whose growing points remain underground for the first few weeks of
growth, and larger, tougher weeds of any species, may lose foliage to the heat, but then regrow.
Keep the vegetable crop weed-free through its “minimum weed-free period” – usually the first
one-third to one-half of the crop’s growing season. Weed-free periods for vigorous summer crops like
corn, squash, or transplanted tomato might be 4–6 weeks, and slower-starting crops like eggplant,
carrot or onion may require 10 weeks weed-free. Weeds that are allowed to grow during this time are
likely to reduce yields significantly, by 10–100 percent. Later-emerging weeds usually have little
direct impact on crop yield. After this point, some weed growth may even help by protecting soil and
providing beneficial insect habitat. However, weeds that harbor diseases or pests of the crops being
produced, promote disease by hindering air circulation, or interfere with crop growth and harvest by
climbing and twining plants, should be eliminated throughout the crop’s life cycle.
Invasive perennial weeds that multiply through rhizomes, tubers, and other vegetative
structures are the toughest to manage, but even they have a window of vulnerability. When the
underground structures have been chopped up by tillage, each fragment regenerates a new shoot, and
initially expends its reserves in doing so. Once it has four or more new leaves, the weed begins to
replenish its reserves, so cultivate again at the 3–4 leaf stage, making sure that shoot growth is severed.
Repeated operations, combined with competition from cover or production crops will eventually
exhaust even the most stubborn perennial weeds.
Remove weeds before they multiply. Cultivate, mow, or pull flowering weeds to prevent seed
set. Some weeds can mature seeds after they have been uprooted, so get them before blooms open to
prevent seed set. Invasive perennial weeds like bermudagrass and Canada thistle can propagate
underground any time they are allowed to grow continuously for more than four weeks, or attain a foot
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or more in height. Perennial weed infestations may require periodic cultivation, chopping, or mowing
throughout the cropping cycle.
Timely application of organic mulch can enhance control of many annual weeds. Once the
crop is established, hoe or cultivate shallowly early on a clear, hot day, let the uprooted weeds die in
the sun, then spread hay or straw mulch that evening or the next day to conserve moisture and
discourage additional weed emergence. This strategy often gives equal or superior weed control for
fewer cultivation passes.
In plastic-mulched crops, monitor planting holes for emerging weeds, and remove them while
still small enough to pull easily. Usually, one weeding is sufficient, after which the crop shades out
later-emerging weeds. Control alley weeds sufficiently to prevent weed propagation, maintain air
circulation around the crop, and facilitate harvest.
Biological controls play a major role in insect pest management in organic and sustainable
farming systems.
Beneficial insect releases and beneficial habitat plantings (farmscaping, or
conservation biological control) often form the foundation of organic insect pest management. What
about biological weed control? Considerable research has been conducted on biological control of
weeds with herbivorous or seed-eating insects, specific microbial pathogens of weeds (“bio
herbicides”), and soil microorganisms that suppress weed germination, emergence, or growth. At this
time, however, few organic vegetable growers utilize weed bio control agents. Although ongoing
research may expand the future role of weed bio control products, they may not ever achieve the
prominence of the many biological insect pest controls that are now widely used.
Most insect pest outbreaks involve one or two insect species attacking a specific crop. Often,
the pests can be controlled through conservation or augmentative release of their specific natural
enemies. In contrast, many different weed species appear each year in the field. A specialist bio
control agent that knocks out one or two species may not significantly reduce overall weed growth,
while a generalist agent that attacks most or all of the weeds present would likely damage the crop as
well. Furthermore, the efficacy of experimental bio herbicides depends greatly on weather, soil, and
other factors that vary widely from farm to farm and from year to year. However, specific weed-eating
insects have been used successfully against several invasive exotic weeds in rangeland and natural
ecosystems (see sidebar next page).
Although organic farmers rarely use biological products or agents in weed control, weeds can
be impacted by several biological processes, including:
•
Herbivory – consumption by livestock, wildlife, or insects
•
Weed seed predation and decay
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•
Disease caused by bacteria, fungi, or other agents
•
Plant–soil–microorganism interactions that modify the competitive relationship between crop
and weed
•
Allelopathy by cover crops or production crops
Understanding these processes and how various cultural practices and weed control measures
influence them can lead to improved organic weed management strategies. Much of this is still in the
“research and discovery” phase.
Weed seed predation by ground beetles and other macroscopic organisms has been shown to
reduce weed seed banks significantly under field conditions (Menalled et al., 2006). Maintaining
organic mulches or vegetative cover year round in part of the field provides habitat for seed predators.
Management strategies to promote weed seed decay by soil micro-organisms have not consistently
shortened the half-life of the weed seed bank. Claims that organic farming or particular approaches to
organic farming directly reduce weed populations or weed aggressiveness by enhancing soil life or
changing the soil nutrient balance (e.g., higher calcium levels) have not been validated through
controlled trials. However, good organic practices and healthy soils can enhance crop vigor, thereby
reducing weed problems.
CLASSICAL BIOLOGICAL CONTROL OF WEEDS
The introduction of insects to combat weeds usually takes the form of classical biological
control or copulative release. Relatively small numbers of an insect that feeds on a specific weed
species, or a closely related group of weed species, are released at several points within the weed’s
range. When the releases are successful, the insects multiply and spread over a number of years,
gradually bringing the weed under control over a wide geographic area.
This approach is most often used against an invasive exotic weed that has become a major
problem in pastures, rangeland, other agroecosystems, waterways, or native plant communities over a
wide region, and is not easily suppressed by other means.
Classical bio control of an exotic weed normally entails a cooperative effort of professionals
from several disciplines, such as entomology, ecology, native plant conservation, weed science, and
range management. Investigators go to the weed’s region of origin to identify, collect, and evaluate its
natural enemies as potential bio control agents. Often, two or three different species are utilized
simultaneously to enhance control of the target weed. Potential bio control insect(s) are carefully
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evaluated in quarantine for a year or more to ensure that they will attack only the target weeds, and
not become pests of crops, native plants, or other nontarget vegetation.
This approach is rarely used in croplands, where many unrelated kinds of weeds occur, and
routine tillage, cultivation, and pesticide use in crops generally interfere with the bio control agents.
However, classical biological control may play an effective role in removing one of the above-listed
invasive plants from pastures, conservation buffers, or field border habitat plantings, especially on
organic farms that use fewer and less-persistent insecticide sprays.
In addition, diversified farming systems that include livestock and/or poultry in addition to
vegetables and other annual crops offer expanded weed management options. For example, if a field
that has been devoted to annual crop production becomes too weedy, rotating the field into perennial
grass–legume pasture or hay for a few years can break the life cycle of the “weeds of cultivation” and
reduce their seed banks. Good rotational grazing practices and haying practices can enhance weed
control and prevent the buildup of perennial pasture weeds during this period. Many farmers who use
such rotations report enhanced yields and reduced weed pressure when the field is returned to
vegetable production.
Grazing livestock in fields immediately after vegetable harvest can help curtail weed growth
and weed seed production, and poultry will consume weed seeds on the soil surface. Livestock can be
useful in removing diseased crop residues that might otherwise require composting, burning, or burial
by inversion tillage for disease control.
Livestock can also be used to graze down understory vegetation in orchards, Christmas trees,
and other tree plantings (silvopasture), a practice that can accomplish weed management, livestock
nutrition, and fertilization (manure) simultaneously. Repeated intensive grazing can clean up a weedinfested field for future crop production. The weeds should be grazed to the point of severe defoliation
at short intervals to deplete underground reserves of perennial weeds. Hogs can be especially effective
against perennial weeds, as they root out and consume fleshy roots, rhizomes, and tubers.
Weeder geese are certain Asian and Chinese varieties of geese that have been used for
centuries to remove young grasses and other weeds from established crops, including berry plantings,
vineyards, and orchards. Weeder geese require water, shade, and fencing for containment and
protection from predators while they are working in the fields. They control weeds most effectively
during their first year of life, and should be introduced to the fields at the age of six to eight weeks.
Older, second-season geese weed much less actively, so it is common practice to utilize the geese for
weed control for one season, and then finish them for meat.
In utilizing farm animals for weed management, be sure to consider what weeds are present,
and the grazing needs and preferences of the livestock. Grazing for weed control works best on weeds
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that provide high quality forage, such as johnsongrass, bermudagrass, quackgrass, crabgrass, pigweed,
and lambsquarters. It will not work for unpalatable species like horsenettle or thistles, and grazing
large amounts of succulent but toxic weeds such as docks and St. Johnswort (=Klamath weed) can
endanger livestock health.
One limitation of livestock for weed control is that most animals do not digest all the seeds
they consume. As a result, their manure can carry or spread weed seeds from field to field. Thus, they
control weeds most effectively when they graze before the weeds set seed.
Finally, it is important to protect food safety when utilizing livestock, poultry, or weeder geese
to manage weeds in food crops. This rule applies to droppings left by livestock, poultry, or weeder
geese, as well as manure applications, and is a good guideline for protecting food safety on all farms.
Running livestock after vegetable harvest and just before cover crop planting, and during the
pasture/sod phase of a long term rotation, are effective ways to utilize animals to manage weeds and
build soil fertility without compromising food safety or organic certification status.
Crop allelopathy against weeds can also be considered a biological effect. In addition to cover
crops, a few vegetable varieties have been shown to exert significant allelopathic activity against
weeds, especially weed seedlings. Many allelopathic relationships are quite specific. For example,
sunflower root extenuates inhibit seedling growth of wild mustard and other broad leaf weeds, but
have little effect on grasses. Sweet potatoes strongly inhibit yellow nutsedge and velvetleaf, but have
relatively little effect on pigweed, morning glory, and coffee senna. In no-till field trials, rye residues
are strongly allelopathic against pigweed and lambsquarters, but not ragweed.
Recently killed rye mulch is highly suppressive against lettuce and other small-seeded
vegetables, much less so for large-seeded vegetables like snap bean, and not at all on transplanted
tomato, pepper, cucurbits or brassicas. Transplants and large seeds are inherently less susceptible to
allelopathic suppression. Furthermore, the allelochemicals given off by cover crop mulch are
concentrated near the soil surface. Transplants and large seeds are planted deep enough so that their
roots escape the zone of high allelochemical concentrations. This tolerance is often utilized in fields
whose weed floras are dominated by small-seeded annuals that germinate from near the soil surface.
For example, tomato and other transplanted summer vegetables often do well in a killed rye + vetch
mulch, which usually provides several weeks’ selective control of many summer annual weeds. As
specific allelopathic relationships become better understood, crop rotations and cover cropping
practices can be designed to give crops an edge over certain weeds.
Healthy soil, optimum nutrition, appropriate planting dates, and best cultural practices enhance
the ability of most vegetables to deal with weed pressure. However, some crops are inherently weedsensitive and require extra attention to protect them from weed competition even in the best of
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circumstances. Factors that make a crop especially vulnerable to weeds include slow early growth, a
long establishment period, and cultural requirements that limit options for managing weeds with
tillage and cultivation.
Weed control in perennial horticultural crops like asparagus, cane fruit, young or dwarf fruit
trees, and some cut flowers can be quite difficult, especially when perennial weeds dominate the weed
flora. Bring existing weed pressure under good control through strategic tillage and intensive cover
cropping before planting perennial vegetable, fruit or ornamental crops. Continue with diligent weed
control during the first few years after planting in order to get the crop well established. Asparagus,
some perennial herbs, and perennial cut flowers do not compete well against weeds, and may continue
to need intensive weed management throughout their lifetimes. Invasive rhizomatous or tuber-forming
perennial weeds pose especially severe problems in perennial crop production. Try to avoid these
weeds through site selection and site preparation for perennial crops.
Site preparation can include tillage methods that will effectively control existing weeds, cover
cropping, sheet mulching (a layer of cardboard or several layers of newsprint plus several inches of
organic mulch), soil solarization (covering the soil with clear plastic for a few weeks during hot
weather to kill weed seeds and propagules in the top few inches of soil), or manual spot-weeding.
Many farmers grow and till in a series of highly competitive cover crops before setting out asparagus
crowns, young berry bushes, or fruit trees. Cover crops that become infested with invasive perennial
weeds or large numbers of other weeds should be mowed, tilled in, and immediately followed by
another cover crop.
Soil pH, nutrient levels, and physical condition should be carefully assessed and adjusted
through appropriate amendments to optimize growing conditions for the desired crop. Good site
preparation and pre-plant weed control can save the grower many days of backbreaking labor digging
and pulling weeds out of the new planting, and can make the difference between success and failure.
Other weed-sensitive crops with shorter life cycles, such as strawberry, onion, leek, garlic,
carrot, and parsnip, require essentially weed-free conditions for at least several months after planting.
Growers often place these in their rotations following highly weed-competitive cover crops, “cleaning
crops” that facilitate weed control and reductions in the weed seed bank, or both. Cleaning crops
include vegetables like potato, sweet potato, corn, cabbage, and broccoli that can be cultivated
vigorously and hilled up early in their life cycle, and compete well against weeds later on. The wide
spaces between rows of winter squash can be cultivated several times to flush out weeds before the
vines spread out; however later-emerging weeds often set seed during the crop’s long maturation
period. For vegetables like carrot and onion, growers often employ fallow cultivation or stale seedbed
for a few weeks before planting to draw down the weed seed bank.
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Organic no-till usually refers to mechanically killing a high biomass cover crop without tillage
(usually roll-crimping or flail mowing), followed by no-till planting of transplanted or large-seeded
vegetable or row crops. Production crop can also be planted no-till into winterkilled cover crop
residues. Examples of this practice include tomato and pepper transplanted into roll-crimped winter
rye + hairy vetch, fall brassicas planted into flail-mowed summer foxtail millet + soybean, and early
spring vegetables planted into winter-killed oats + peas. Because continuous no-till is not practical in
organic production, fields are normally tilled after vegetable harvest before planting the next cover
crop, and the system is properly known as “rotational no-till.”
Whereas these reduced-tillage systems can enhance soil quality, reduce flushes of annual
weeds, and give good vegetable yields, they commonly fail when perennial weeds are present or
overall weed pressure is high. Nutsedges, quackgrass, bermudagrass, johnsongrass, Canada thistle,
bindweeds, and even small clumps of fescue, timothy, and clover left from recently turned sod crops
will readily grow through the heaviest of cover crop mulches and compete severely with no-till
planted vegetables. High populations of annual weeds or a large seed bank of annual weeds can also
spell trouble. Rotational organic no-till should be considered a “weed-sensitive system,” and existing
weeds should be brought under control first before attempting no-till cover crop management.
WEED MANAGEMENT CHECKLIST FOR PERENNIAL AND OTHER WEED-SENSITIVE
CROPS
Nothing in this information sheet can tell you as accurately how to manage the weeds on your
farm, as your own observation! Keep watching the weeds through the season and year after year.
Some weeds may indicate certain soil conditions, such as nutrient imbalances, compaction, or poor
aeration. There is a lot of traditional lore on this subject – some well substantiated and some less so.
Several books have been written on this topic, but again your observations are probably the best guide.
In general, increasing problems with annual weeds may result from frequent tillage on a
“predictable” schedule, so reduce tillage or vary timing and method, and consider rotating weedy
fields into perennial cover or pasture for a few years.
Also try overseeding cover crops into
established vegetable or row crops at the time of last cultivation.
Some annual weeds, including pigweeds and foxtails, have adapted to no-till systems, and will
emerge in untilled fields, especially when the soil is mostly bare. Increase ground coverage or till
strategically to address the problem. If summer annual weeds get bad in warm season vegetables,
rotate to cool season vegetables and competitive summer cover crops. If winter annual weeds become
a problem in cool season vegetables, rotate to summer vegetables and vigorous winter cover crops.
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If you use the moldboard plow or other inversion tillage regularly, and large seeded annual
weeds such as velvetleaf, common cocklebur and morning glories are your biggest headache, consider
switching to shallow, non-inversion tillage. On the other hand, if you rely on the rototiller, and smallseeded weeds with short lived seeds, such as galinsoga are building up to unmanageable populations, a
one-time pass with the moldboard plow may bury much of the weed seed bank to a depth from which
seedlings cannot emerge, and at which the seeds gradually die. This strategy has even been used with
fair success against moderately long-lived seeds, such as pigweed. Be sure to keep subsequent tillage
quite shallow for a few years after plowing to avoid exhuming the seeds while they are still viable.
Increasing problems with invasive perennial weeds may indicate a need for increased tillage
for a period of time to bring these problem weeds under control. Consider the root / rhizome structure
and specific vulnerabilities of the target weed when choosing tillage implements. For example, a
chisel plow can effectively bring quackgrass, bermudagrass, or nutsedge rhizomes to the surface to dry
out or freeze, but can be ineffective or even counterproductive for deeper-rooted invasive perennials
like Canada thistle. Follow tillage with vigorous, weed-smothering cover crops to minimize soil
degradation and to enhance weed suppression. If an asparagus bed or berry patch has become infested
with these weeds, consider tilling it up and rotating the area into annual crop production.
Transplanting the perennial crop root crowns to a clean site before destroying the weeds may or may
not be cost effective, depending on crop vigor and size of planting.
Carefully observe the timing of heaviest weed emergence and growth, and consider shifting
planting schedules so that your crops miss the most intense weed competition. Many growers delay
planting for a couple of weeks to allow the late spring flush of weeds to come up, to be destroyed
during seedbed preparation. The long growing seasons in the South allow considerable flexibility in
adjusting planting date to avoid times of peak weed emergence. In comparison delaying planting in the
upper Midwest or Northeast may result in a yield reduction because of the short season..
When dealing with weeds organically, don’t be afraid to try something new! You may read
about a new weed control tool, NOP-allowed herbicide or bioherbicide, cover crop, or crop rotation
strategy in a farm magazine that sounds like it might be worth trying on a tough weed problem on your
farm. You might think of a novel way to use, combine, modify or fabricate cultivation implements to
better match your cropping system or weed complex. Or, you might come up with an entirely new
strategy to give the crop the advantage. Try out any of these ideas by conducting a simple on-farm
experiment. Farmer innovation and on-farm trials are the time-honored way that humankind has made
advances in farming and food production.
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Nighttime Cultivation
Because tillage exposes weed seeds to a light flash, cultivation to remove existing weeds is
often followed by a new flush of weeds. This can result in a soil-exhausting “cultivation treadmill” if
the soil’s weed seed bank is large. Some growers and researchers have experimented with cultivating
at night or with an opaque cover over the tillage implement. This eliminates the light stimulus, and has
reduced subsequent weed emergence, usually by 20–70 percent.
Soil Solarization
Covering the soil surface with clear plastic mulch during hot sunny weather can raise the
temperatures of the top few inches of soil sufficiently to kill vegetative propagules (e.g., rhizomes of
johnsongrass) and some weed seeds. A few growers use this method on a small scale to prepare beds
for high value specialty crops. Soil solarization is not so effective on dormant or “hard” weed seeds,
or on any seeds or propagules buried at a depth of six inches or more.
Nutsedge tubers are quite heat tolerant (to about 120°F) and difficult to kill by solarization;
however solarization induces wide fluctuations in soil temperature that break nutsedge tuber dormancy
(Chase et al., 1999). Tips of emerging shoots open, become trapped, and are heat-killed under the
plastic, which can significantly weaken the tubers, and facilitate control by subsequent cultivation.
Biological Weed Controls and Organic Herbicides
Several organic (OMRI approved) herbicides based on plant allelochemicals or essential oils
are commercially available. They are fairly expensive and are most practical for spot applications such
as clearing weeds from around a farm stand or dealing with a localized infestation of a noxious weed.
Researchers have also developed bio herbicides based on specific plant pathogens. Two
products – DeVine against stranglervine in citrus, and Collego against northern jointvetch in rice and
soybeans, achieved commercial success in the 1980s. These products are now off the market because
the target weeds were largely eliminated, and demand for the products dried up. Other bioherbicide
agents against pigweeds, hemp sesbania, and sickepod have shown promise in research trials, but are
not yet commercially available. Researchers continue to seek new bio control agents for new invasive
exotic weed problems.
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Crop–Weed–Soil–Microbe Interactions
Some fascinating research has been done into the role of soil and root-zone microorganisms in
plant–plant interactions and the so-called “rotation effect.” Microbes play a role in many specific
crop–weed interactions, forming beneficial symbioses with some plants while inhibiting or
parasitizing others. For example, mycorrhizal fungi are highly beneficial to legumes, grains, onion
family, cotton, strawberry, and many other crops; but are mildly parasitic to weeds and crops in the
amaranth, buckwheat, chenopod (spinach, beet, lambsquarters), and purslane families, purple and
yellow nutsedges, and a few weedy grasses like annual bluegrass. Studies have shown that high
populations of mycorrhizae in the soil can slow the growth of some of these “non-host” plants, which
suggests that mycorrhizae could give “strong-host” crops like grains, legumes and onion family an
edge over non-host weeds like pigweeds, lambsquarters, and nutsedges. This possibility merits further
investigation.
Brassicas (cabbage, broccoli, turnip, Asian greens, radishes, cultivated and weedy mustards)
defend themselves against most fungi, including mycorrhizae, through release of allelopathic
glucosinolate and isothiocyanate compounds. Whereas some researchers are attempting to give crops
an edge over weeds by adding certain microbes to the soil, the existing microbiota in most soils is
likely to overwhelm the added inoculant. Direct inoculation of the roots of strong-host crops with the
correct mycorrhizal symbiosis may be an exception, and has sometimes shown promising results. One
future practical application of soil microbiology research may be to fine-tune crop rotations, soil
amendments, and management practices to optimize soil microbiota for the crop and thereby give it an
advantage over weeds.
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179
V.
DIVERSIFIED AND INTEGRATED FARMING SYSTEMS
EFFECT OF CASSAVA ON SOIL PRODUCTIVITY
Like any other crop, cassava absorbs nutrients from the soil and at harvests all or parts of
these are removed from the field, resulting in nutrient depletion and fertility decline. In addition,
soil/crop management, such as land preparation and weeding, can lead to soil compaction or to soil
erosion, which results in soil loss and nutrient losses in eroded sediments and runoff.
Nutrient Removal by the Cassava Crop
Data reported in the literature on nutrient absorption and removal by cassava and other crops
vary greatly, depending on the fertility of the soil, the yields obtained, and the plant parts removed in
the harvest. K removal per ha was higher than other crops, but K removal per t DM produced was also
similar or lower than those of other crops. Thus, it is clear that cassava does not remove more
nutrients from the soil than other crops, with a possible exception of K.
If farmers remove from the field not only the roots but also stems, leaves and fallen leaves,
they will remove substantial additional amounts of N, Ca and Mg, since 75% of N, 92% of Ca and
76% of Mg were found in the plant tops and fallen leaves, and only 25%, 8% and 24%, respectively,
in the roots. In case of P, about equal parts were found in roots and tops, while for K about 60% was
found in the roots and only 40% in tops and fallen leaves. Thus, if only roots are removed, the ratio of
N, P, K removed (in terms of N, P2O5 and K2O) is 1.8:1:3.8 or about 2:1:4, while if all plants parts are
removed this will be 3.3:1:2.9 or about 3:1:3.
Since nutrient removal is mainly a function of yield, it is more practical to calculate nutrient
removal per ton of fresh roots harvested.
Cassava extracts relatively small amounts of P in the roots as well as the tops, while farmers
apply rather high doses of P in pig manure and SSP. This is a waste of resources and may lead to P
pollution of waterways and lakes. In case of N, the balance is positive in some but negative in other
regions. Considering that large amounts of N are usually lost by leaching or volatilization, it is likely
that the total balance is negative and that soils also become depleted of N. This, however, can be
partly offset by incorporation of residues of leguminous inter crops, such as peanut, or of prunes of
hedgerow species, such as Tephrosia candida. The P and K in these residues must come from either
the soil or from added manures or fertilizers; these should therefore not be considered as an “input”
into the system, but merely a recycling of these nutrients within the system. The latter can be of value
in case of deep rooted leguminous species, which can bring nutrients from deeper soil horizons back to
the surface; it is doubtful that inter crops like peanut or black bean contribute much in this respect.
The off-take of dry grain will generally result in a negative rather than a positive contribution to the
nutrient status of the soil.
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Erosion as a Result of Cassava Cultivation
Cassava is oftentimes blamed for causing severe erosion when grown on slopes. There is no
doubt that cassava cultivation, like that of all annual food crops, causes more runoff and erosion than
leaving the land in forest, in natural pastures or under perennial trees. This is mainly due to the
frequent loosening of soil during land preparation and weeding, as well as due to the lack of canopy
and soil cover during the early stages of crop development. The question is whether cultivation of
cassava results in more or less soil loss than that of other annual crops.
Compared with other crops cassava establishes a canopy cover only slowly, often requiring 34 months to reach full canopy cover. Moreover, the cassava canopy cover is effective only in
protecting the soil from rainfall-induced erosion, but is not effective in reducing runoff-induced
erosion, which occurs near the soil surface, and which becomes increasingly important as the slope
increases. This may lead to increased erosion. On the other hand, cassava does not need intensive
land preparation and a smooth seed bed like many seeded crops, nor does it require more than one land
preparation per year, compared with 2-3 times for short-cycle crops like most grain legumes, maize
and sorghum. Moreover, once the canopy is established there is no more need for weeding, while the
canopy is effective in reducing raindrop impact, and thus erosion.
Thus, it may be concluded, that in most (but not all) cases cassava cultivation on slopes causes
more erosion than that of other crops, mainly due to the wide plant spacing used and the slow initial
growth of the crop, resulting in slow canopy development. This effect is exacerbated if there is
excessive land preparation and weeding (as in some areas of north Vietnam), poor germination due to
low-quality planting material, and slow initial growth due to lack of adequate fertilization.
Nutrient Losses in Eroded Sediments and Runoff
When soil particles are dislodged by the impact of raindrops or by the scouring action of
overland flow, and move down-slope with runoff, the field not only loses the most fertile part of the
soil, i.e. the topsoil, but also associated organic matter, manures, fertilizers and beneficial microorganisms, such as mycorrhizal fungi. Moreover, clay particles, once dislodged, are quickly carried
downslope, resulting in a preferential loss of clay and a lightening of soil texture. This may be the
reason why soils used for a long time for cassava cultivation were found to be much lower in clay,
organic C and CEC than those used for forest, rubber or cashew.
In addition, applied fertilizer particles can be dislodged and removed, or the water-soluble
constituents can be lost with runoff water. In general, it was found that eroded sediments are much
higher in nutrients than the soil in the original site. This enrichment is due to preferential losses of
organic matter, clay, earthworm castings and plant debris laying on the soil, or by dissolved manures
or fertilizer. Thus, erosion does not only reduce the soil depth available for root growth and for uptake
of nutrients and water, but it also leaves the remaining soil less fertile, while often exposing highly
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infertile subsoils. This has a detrimental effect on productivity, where cassava yields on eroded soil in
Colombia were about half those on nearby non-eroded soil.
Little quantitative information is available on actual nutrient losses in sediments and
runoffThe latter practice markedly reduced runoff and erosion, especially in the second year of
establishment. K losses were particularly high in both runoff and erosion during the first year of
cropping, but decreased markedly in the second year, especially with alley cropping. N and P losses
were always higher in the sediment than in runoff, but K losses were always higher in the runoff.
During two years of upland rice production using the farmer’s practice, 80.4 kg N, 12.9 kg P and
172.3 kg K/ha were lost in eroded sediments and runoff; for the alley cropping treatment this was
reduced to 25.0 kg N, 4.1 kg P and 108.6 kg K/ha. Thus, substantial amounts of nutrients, especially
K, were lost in eroded sediments and runoff.
CROP/SOIL MANAGEMENT PRACTICES TO MAINTAIN OR IMPROVE SOIL
PRODUCTIVITY
Fertility Maintenance
To maintain or improve the productivity of soils used for cassava cultivation, it is necessary to
reduce nutrient losses by crop removal and erosion, and prevent physical deterioration through
excessive land preparation (especially with heavy machinery), and loss of clay and organic matter
through erosion. In addition, the nutrients and organic matter lost should be replaced by application of
fertilizer or manures, or by incorporation of green manures or inter crop residues.
Chemical fertilizers
Nutrients removed in harvested products, in runoff and eroded sediments can be replaced by
application of chemical fertilizers. Moreover, although cassava can grow on poor soils, the crop is
highly responsive to fertilizer applications. While in most cases there is a yield response only to the
application of N, P and K, in some cases, especially if plant tops are also removed, there may also be a
yield response to the secondary (Ca, Mg, S) and micro-nutrients (especially Zn).
Nutrient concentrations in plant tissues vary continuously during the crop cycle and are very
different for different plant parts (leaves, petioles, stems) and location within the plant (upper, middle
or lower part) (Howeler and Cadavid, 1983). For that reason, for diagnostic purposes, only the
“indicator” tissue, i.e. the youngest fully-expanded leaf (YFEL) blades (without petioles), are collected
at 3-4 months after planting (if in the wet season); these samples are quickly dried in the sun or in an
oven at 60-80oC for 1-2 days; after grinding in a mill they are sent to the laboratory for analysis.
In the absence of laboratory facilities, a rough estimate of nutritional requirements can also be
obtained from simple trials on farmers’ fields using three rows each of the following treatments:
N0P0K0, N0P1K1, N1P0K1, N1P1K0, and N1P1K1, where N0, P0, K0 indicate without N, P or K, and N1,
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P1, K1 correspond to about 100 kg N, 40 P2O5 and 100 K2O/ha, respectively, using urea, SSP and KCl
as the nutrient sources; animal manures should not be applied in these trials. The yields of the center
row of each treatment will give an indication of the relative importance of the three nutrients, after
which more detailed trials can be conducted to determine the optimum amount(s) of the mosts
important nutrient(s).
Organic manures
Especially in the Red River Delta and in the northern part of the Central Coast, farmers are
accustomed to applying 4-10 t/ha of manure, mostly pig or buffalo manure, to cassava. The nutrient
contents of these manures are seldom known and are highly variable. On average, chicken manure
seem to be relatively high in N, K, Ca and Mg, while pig manure is relatively high in P. Wood ash,
water hyacinth and rice husks are all good sources of K, while wood ash is also very high in Ca and Mg.
Manures are thus a major and indispensable source of nutrients for cassava, while also
contributing organic matter and improving the physical conditions of the soil.
These manure
applications are particularly important when farmers remove all plant parts from the field, as they help
restore soil organic matter and supply secondary and micro nutrients.
Farmers’ practice of very high applications of FYM combined with low rates of N, P and K as
chemical fertilizers did not result in maximum yields or profits. Highest yields and net income are
probably obtained with modest (5-6 t/ha) of manure combined with about 60 kg N and 120 K2O/ha,
either without or with 30-60 kg P2O5/ha. Applications of Mg as fused Mg-phosphate are probably
necessary in case no FYM is applied at all.
Green manures and alley cropping
Few experiments have been conducted in Vietnam to determine the effectiveness of planting
and then incorporating a crop of green manure before planting cassava. In north Vietnam where farm
size is small, few farmers will want to plant a non-productive crop for the sole purpose of improving
soil fertility. However, in remote areas where land is abundant but fertilizers or manures are not
available, this may be an attractive option. Moreover, the green manure may help to smother out
Imperata cylindrica grass.
Experiments with various green manure species conducted in Thailand showed that
incorporation of Crotalaria juncea, Canavalia ensiformis, Mucuna sp and pigeon pea increased
cassava yields when no fertilizers were applied, but had no significant effect on yield in the presence of
fertilizers.
Alley cropping cassava with contour hedgerows of Tephrosia candida is a well-established
practice in some parts of north Vietnam. It is used to control erosion as well as to improve soil fertility
when the prunes of the hedgerows are mulched or incorporated. Thai Phien et al. (1994) reported that
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Tephrosia hedgerows produced on average 0.5-1.0 t/ha/year of dry biomass for incorporation into the
soil, which may contribute 10-20 kg N/ha. This compares with 1.5-2.0 t/ha of dry residues of inter
cropped black bean supplying 35-40 kg N/ha, or 4-5 t/ha of dry residues of inter cropped peanut
supplying 50-70 kg N/ha. Only part of this N is added to the system through biological N fixation by
the legumes.
inter cropping
inter cropping with maize also reduced cassava yields about 20-25%. Profits were highest for
cassava monoculture or inter cropping with peanut (Nguyen Huu Hy et al., 1995).
inter cropping and hedgerows reduced cassava yields, but the additional income from the
peanut more than compensated for the lower income from cassava.
inter cropping with peanut
generally produced higher net income for the farmer than inter cropping with other crops or mono
cropping.
Erosion Control
Numerous erosion control trials conducted in both north and south Vietnam have shown that
runoff and erosion losses can be markedly reduced by inter cropping and planting of contour
hedgerows. inter cropping with peanut was generally more effective in reducing erosion than inter
cropping with other crops, due to the rapid formation of soil cover. Contour ridging and no- or reduced
tillage were also effective in reducing erosion, while adequate fertilization also helped to reduce
erosion.
However, contour ridging, fertilization and inter cropping require more work and usually imply
higher production costs. Hedgerows also require more work in establishment and maintenance and
may reduce yields by occupying 10-20% of the land. Thus, farmers have to consider the trade-off
between immediate costs and benefits versus long-term benefits of less erosion and improved fertility.
TRANSFER OF TECHNOLOGIES
While many management practices to control erosion have been recommended by researchers
and extension agents, few of these practices have actually been adopted by farmers. This is mainly
because most of the recommended practices require either additional labor or money, and benefits are
usually accrued over the long-term, while most poor cassava farmers are in desperate need of
immediate income to feed their families.
The NPV for the first two years was very low due to the high initial costs of establishing the
hedgerows, the costs of maintenance and the lower maize yields obtained. Thus, the farmer will not
receive economic benefits from planting hedgerows until after about five years. It is only after 10-15
years that farmers will reap substantial economic benefits from these soil erosion practices, but that is
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too long for most farmers with a short planning horizon, or with immediate needs for adequate income.
This example shows the main dilemma in promoting soil conservation practices: most recommended
practices were selected by researchers because they are effective in controlling erosion, but few
consider whether poor farmers can actually bear the economic burden of adopting these practices. If
they can not, governments may have to provide some incentives, since part of the benefits of better
erosion control are reaped off-site by people living downstream or in the cities.
Another problem in the transfer of soil conservation technologies is that many soil erosion
control trials were conducted on experiment stations under optimum and uniform conditions. These
conditions seldom correspond with those faced by farmers living in mountainous areas with
heterogeneous soils, topography and climates, and with economic opportunities that vary markedly
from place to place depending on distance to roads and markets. Many practices that seemed very
effective in controlling erosion, and may have economic benefits under the conditions of the
experiment station, may be rejected by farmers simply because they are not effective or not appropriate
under the farmer’s specific biophysical and socioeconomic conditions. For that reason it is more
effective to present farmers with a range of options, from which they can select those that they consider
useful, and let them try out some of these options on their own fields; this way farmers can observe and
decide which is the most effective and useful practice for their own conditions.
This farmer
participatory research (FPR) methodology is particularly useful for developing and disseminating
technologies like erosion control practices that are highly site-specific and where there are many tradeoffs between costs and benefits. Only farmers themselves can decide about the costs they can bear and
the risks they can take now in order to obtain benefits sometime in the future.
FERTILIZING THE FIELDS WITH DUCKS
Experts and practitioners across Asia have for a long time reflected the application and often
overuse of chemical fertilizers, herbicides and pesticides. Scepticism about the outcomes of
agricultural practices that use these chemical inputs grew over time, because of the high costs for
chemical products and the perceived negative effects of artificial chemicals for the environment. The
pesticides seemed, for instance, not to prevent the appearance of nasty insects, and their stings were
causing even more.
What was done to solve it?
The method works in the following way (Ho 1999; Xu 2006): Two-week-old Aigamo
ducklings are introduced into a rice paddy about one or two weeks after the seedlings have been
planted. The number of ducklings can vary.
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A shelter is needed where the ducklings can rest. The field should provide protection for the
ducks from dogs, cats, weasels, raptors etc. The ducks are left in the fields all the time, where they can
range completely free. The situation changes once the rice plants form ears of grain. Then the ducks
have to be taken away to prevent them from eating the rice grains. They have then to be fed to mature
and lay eggs. Waste grain is an option. In addition to putting ducklings on the paddy-fields, an aquatic
fern (Azolla microphylla) is introduced which grows on the surface of the water. The azolla fixes
nitrogen and serves as duck feed. The plant also provides shelter for the fish (i.e. roach) which can also
be introduced and which feed on duck faeces, daphnia and worms. The fish and ducks provide manure
to fertilize the rice plants and stimulate through the turbulences they cause when moving the plants to
grow stronger stems. The rice plants are thus not only less vulnerable to storm but in turn provide
shelter for the ducks and fish.
Scientific analyses show that this system has a positive effect on the improvement of soil
fertility and the conservation of the biodiversity for instance of the diversity (not the number) of
arthropod communities.
INTEGRATED FARMING IS PROFITABLE
This method of farming varies according to the climate, water availability, fish species, plant
variety, and traditional custom. In some places, agricultural crops other than rice are integrated with
fish farming. The Garin integrated farm at Barangay Igcocolo, Guimbal, Iloilo has a different style of
raising tilapia with agricultural crops and livestock. The 7-hectare farm is planted to rice or corn (4 ha),
and formerly to citrus (3 ha). Poultry with 10,000 layers and 5,000 broilers are housed just above the
rice fields. Adjacent to the poultry are two tanks (approximately 10 x 8 x 1.5 m each) stocked with
tilapia and fertilized by chicken manure. Water continuously flows through the tanks and down to the
rice fields. Thus, waste from poultry goes through the tilapia tanks and then to the rice plants. Mr.
Narciso Tadifa, DA agricultural technologist and nursery-in-charge, says that the tilapia grows to as
big as a man’s palm and is marketed live at a beach resort (P12 per 100 g). Sometimes, excess
production is sold to other business establishments in Iloilo City. The farm also grows sheep and cattle.
Although both farms claim profitability, some rice-fish students from the University of the
Philippines at Los Banos and the Central Luzon State University say that yield of tilapia in rice-fish
culture is very low because of low recovery and poor growth rate. In their studies, absolute growth rate
was 0.10 g per day per fish making only 26.7 g after 85 culture days. The study attributed the poor
growth of tilapia to the unfavorable water condition at the later stage of the growing period. Partial
decomposition of the rice straw and leaves which changed the appearance of water from clear to dark
color could have led to fish kills due to lack of oxygen. Other students mention the problem of
decreased rice yield mainly because of the unplanted areas given over to fish refuges within the field.
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AQD has its own version of integrated farming. Veering from its focus on knowledge
generation to research utilization, the Technology Verification Project of the Training and Information
Division is evaluating the economic feasibility and profitability of farming mud crab in tidal flats with
existing mangroves.
A part of the 70-ha area planted to mangroves (Rhizophora) in 1990 and 1995 was chosen as
the site for the mud crab project in New Busuang, Kalibo, Aklan. The Kalibo Save the Mangrove
Association (KASAMA) Cooperative spearheads the planting, monitoring and maintaining the
mangroves with funding from the Department of Environment and Natural Resources and USWAG
Foundation. About 10% of the area is covered by canals 80 cm deep for the retention of water at
lowest tide. The height of the enclosure is 30 cm higher than the highest high tide.
The study tests the stocking density (0.5 or 1 per m2) and feed (fish by-catch or mixed diet of
75% brown mussel flesh and 25% fish by catch) of mud crab stocked in the 200 m2 pens. Two months
from stocking (initial body weight, 16-25 g; carapace length, 3-4 cm), the mud crab have attained a
body weight of 65-106 g and carapace length of 5-6 cm.
The site is favorable to the study because of an enlightened population. The vast area (70 ha)
planted to mangrove testifies to the successful cooperation between people, the government and a nongovernment organization (NGO). Mr. Frank Sotuniel, President of KASAMA, says that since the
mangrove have been planted, people from other towns gather mud crab, rabbitfish, oysters, blood clam,
gobies, etc.
THE EXTRACTION OF MIMOSINE FROM IPIL-IPIL
Leucaena leucocephala, otherwise known as ipil-ipil in the Philippines, leaves are used in
cattle, poultry and swine feed and have been tried as a food ingredient in some fish diets (Glude, 1975).
While ipil-ipil contains relatively high amounts of protein, its use as feed has been limited because of
the presence of a toxic substance, mimosine, a lysine derivative, B N-(3 hydroxy- pyridone-4)aminoproprionic acid.
To find a cheap and practical method of extracting mimosine, 50 g each of fresh leaves of
local and Peruvian varieties were handpicked, separated from the stems and soaked in 250, 500, 750 or
1,000 mL of fresh tap water. The leaves were soaked for 24 hours with occasional stirring. After
having determined the amount of water that would give maximum extraction of mimosine, leaves
were soaked in 500 mL of tap water for 6, 12, 18, 24, 30, 36, 42 and 48 hours. After the soaking
period, water was drained and leaves were airdried for one or two days depending on the prevailing
weather condition.
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Soaking leaves in water was a highly efficient method for the extraction of mimosine.The
amount of water used (250, 500, 750 and 1000 mL) did not significantly affect the amount of
mimosine extracted from the local variety (P <0.01). Similar results were obtained when Peruvian
leaves were soaked in water up to 750 mL. Significantly less mimosine was ex- tracted from the
Peruvian leaves soaked in 1,000 mL of water (P < 0.01).
The longer the soaking time the more mimosine was extracted from the leaves. There was an
exponential relationship between the amount of mimosine extracted and the duration of soaking for all
the three varieties. Results show that more than 90% of mimosine was extracted from the leaves after
soaking for 42 hours. When the leaves were soaked for more than 24 hours, there was a need to change
the water to avoid fermentation of the leaves and a foul odor.
Mature leaves contain significantly less mimosine than immature leaves. Results showed that
extraction of mimosine from immature leaves was significantly more difficult than extraction from
mature leaves (P < 0.01). More mimosine was apparently extracted from mature leaves soaked in tap
water than in distilled water, although no significant difference was noted. On the contrary,
significantly more mimosine was extracted from immature leaves soaked in distilled water than in tap
water (P <0.01). When a mixture of leaves was soaked in either type of water no significant difference
was observed in the amount of mimosine removed.
INTEGRATED FISH FARMING
Integrated fish farming combines fish, swine, poultry, and vegetable production. Chicken
coops and pens for pigs and ducks can be constructed on the dikes or above the ponds. Fresh animal
manure thus enters the pond directly, hastening the growth of natural food organisms for the fish being
cultured in the pond. Moreover, livestock feeds that fall into the pond can be directly utilized by the
fish.
Animal manure can also be used to grow fodder crops on the sides of dikes such as squash for
its chopped-up leaves to feed herbivorous fish. And adjacent vegetable plots can be fertilized by the
nutrient-rich pond water. Integrated farming thus brings aquaculture to resource-poor, small-scale
farmers who cannot afford expensive farm inputs. Recycling by-products of animal husbandry greatly
lowers the cost of fish production.
Item One: Milkfish, Tilapia, Shrimp Plus Chickens
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In 1984-86, the Leganes Research Station of the SEAFDEC Aquaculture Department
developed the polyculture of milkfish, tilapia, and shrimp with poultry. The fish swim in the water and
the chickens grow to slaughter-size in poultry houses built above the water.
The two forms of husbandry mesh well in the biological food chain. Chicken droppings that
pass through a welded-wire floor in the poultry house into the water below become a fertilizer for
plankton, the natural food organisms on which fish feed. The milkfish, tilapia, and shrimp then thrive
on the plankton. Further research showed that a 4m x 8m poultry house was right for a 1000 m2 fish
pond. A bamboo catwalk connected the poultry house to the dike. Stocking in the pond consisted of
200 milkfish fingerlings, 1 500 tilapia fingerlings, and 5000 shrimp juveniles - and above it, 90 3-wk
old chicks were put in the poultry house. This mix was found to give the best productivity.
The chickens were harvested after 45 days - half the period for the fish. Two chicken crops
were harvested for one fish crop. At harvest time, farmers who go into polyculture have both fish and
chickens for household food and for sale. For sanitation, it is suggested that chickens be harvested a
week before the fish, and the pond water, immediately changed. When the fish are harvested after
another week, the pond has the healthy smell of fresh fish.
Item Two: Fish-cum-Duck Farming
The dikes of grow-out or 2-yr-old fingerling ponds are partly fenced to form a dry run and part
of the water area or a corner of the pond is fenced with used material to form a wet run. The net pen is
installed 40-50 cm above and below the water surface to save net material. In this way, fish can enter
the wet run for food and ducks cannot escape under the net. In a large pond, a small island is
constructed at the center of the pond for demand-feeding facilities. Stocking densities in China are
higher than those in other countries, averaging 4.5 individuals/m2 of pen shed including the dry run
and 3-4 individuals/m2 for the wet run.
In the early years of integrated fish-cum-duck farming, ducks went everywhere in the fish
ponds to feed; this pattern has been improved. The duck-raising area has been set up to connect the
duck shed, the dry run, and the wet run. Whether fish-cum-duck integration succeeds or not primarily
depends on technical measures of duck raising. Both meat and egg-laying ducks can be raised in
fishponds. In the summer, 14-day ducklings are accustomed to life on the water surface. The food
stocks of meat ducks grow quickly, reaching marketable size (2 kg) in fishponds in 48-52 days; slowgrowing stocks need 55-56 days. Ducks should be marketed as soon as they reach the marketable size
or they will lose their feathers, resulting in decreased food efficiency, body weight, and commodity
value.
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The number of ducks to be raised in fishponds depends on the quantity of excreta per duck,
which, in turn, depends on the species of duck, the quality of feed applied, and the method of raising.
In raising Beijing ducks, about 7 kg excreta/duck can be obtained during the 3-day fattening period.
The egg-laying Shaoxin ducks raised in Wuxi annually produce 42.5-47.5 kg manure/duck; hybrids of
Shaoxin and Khaki-Combell ducks annually produce more than 50 kg/ duck. The stocking rate of
ducks also depends on climatic conditions and the stocking ratio and density of the various fish species
in the pond. In Europe, the stocking rate is usually around 500 individuals/ha. As a result, the
increment of fish yield will be 90 kg/ha. In tropical and subtropical zones, it has been recommended
that the stocking rate should be 2250 individuals/ha. In Hong Kong, the optimum stocking rate is
2505-3450 individuals/ha; in Wuxi, 2000 individuals/ha. For meat ducks, the stocking rate should be
reduced because of the greater production of excreta. In the Taihu district, 7 or 8 fish species are
polycultured in fish ponds. The stocking ratio of the various species remains unchanged when ducks
are raised. If the number of ducks exceeds 3000/ha, filter-feeding fish and omnivorous fish should be
increased and herbivorous fish should be reduced.
Organic-material stacking won't occur in fish-cum-duck integration on the fishpond as long as
the stocking rate of ducks is appropriate and the amount of excreta does not exceed the transforming
power of the fishpond. Ducks swim loosely in the wet run to search for food, their excreta drop evenly
into the wet run, and the fertilization effects of the droppings are felt throughout the pond.
Item Three: Fish Culture with Pig Raising
Fish culture combined with pig raising is a traditional integrated fish-farming practice in rural
China. Combining pig raising with duck raising and fish farming, not only increases economic
efficiency but also increases social and ecological efficiency. The leftovers and residues from kitchen,
aquatic plants, and products and wastes from agriculture and side occupations are often used as pig
food. Pig excreta, in turn, are used as organic manure in fishponds. Pork is a main subsidiary food of
the people in rural China, and pig excreta make a high-quality manure.
There are two types of pigsties in China: the simple pig shed constructed on the pond dyke or
over the water surface and the centralized hog house. Both types have advantages and disadvantages.
The simple pigsty is more suitable for households because of its lower cost and because of small-scale
farms. The pig excreta can automatically flow or be flushed into the fishponds; this saves much labor.
If the area of a fishpond is less than 8 mu,* a pigsty can be set up on the pond dyke and pig wastes will
flow directly into the pond. If more than 30 pigs are raised on the same spot, there is too much manure
for the direct-flow method. Manure is often heaped near the pigsty, causing a partial deterioration in
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water quality. Fish surfacing increases (dissolved oxygen content decreases) when pig manure sinks to
the bottom of the pond or when too much manure flows into the pond.
Centralized hog houses are suitable for large-scale integrated fish farms. After dilution, the
manure can be spread along the pond dyke manually from a small boat. In a large fish pond, the use of
a boat and a mechanical spreading apparatus will facilitate application of manure. In fish-cum-pig
integration, the water quality must be constantly monitored because of the dissolved oxygen problem.
Besides, the production period of pigs should match the demand of pig manure in fish farming.
Item Four: Fish-cum-Aquatic Plant Integration
Fish farmers in southern China often culture aquatic plants in lakes, rivers, waterlogged areas,
or inlets and outlets of irrigation canals. The principal aquatic plants cultured are the water hyacinth
(Eichhornia crassipes), water lettuce (Pistia stratistes), and water peanut or alligator weed
(Alternanthera philexeroides).
Water hyacinth is known as the “king of aquatic plants.” Per unit area, it produces 6-10 times
more protein than soybean. Aquatic macrophytes are easy to manage with less labor and lower costs.
One person can manage about 50 mu of three aquatic plants and can produce 13.1% (dry weight)
crude protein in 6 months.
The three aquatic plants are especially good for rearing fingerlings of silver and bighead carps.
The plants should be mashed into a paste, but the residue could not be removed.
Nutrient contents of three aquatic plants
Nutritional Elements in Pig and Poultry Manure
Pig manure includes much organic matter and other nutritional elements such as nitrogen,
phosphorus, and potassium and is a fine, complete manure. Pig feces are delicate, containing more
nitrogen than other livestock feces (C:N=14:1), making them more susceptible to rotting. The major
portion of pig urine is nitrogen in the form of urea. It decomposes easily.
Nutritional elements in pig manure
Poultry manures include the feces of chickens, ducks, and geese, and are rich in both organic
and inorganic matter. Poultry manures rot quickly and their nitrogen is mostly in the form of uric acid,
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which cannot be absorbed directly by plants. Accordingly, poultry manures are more effective after
fermentation. The annual amount of excrement per fowl is as follows: chicken, 5.0- 5.7 kg; duck, 7.510.0 kg; goose, 12.5-15.0 kg. Although the annual excretion of each is comparatively small, the
quantity of poultry culture is often great; therefore, the total amount of feces is significant.
Swine Manure as a Dietary Ingredient
Chinese integrated fish farms combine polyculture of carps with organic fertilization derived
from agriculture. A study examined the response of a polyculture of silver, bighead, common, and
Crucian carps to varying amounts and frequencies of fermented pig manure application.
Net fish yield averaged 10.2 kg/ha/d with an average manure application rate of 31 -48 kg dry
weight /ha/d. Daily manuring increased net fish yields by 38% over applying manure at 5- or 7-day
intervals. Silver carp accounted tor 62% of this increase. Net fish yield was directly proportional to the
amount of manure applied over the range 0-48 kg dry weight manure/ha/d. Net fish yield increased 1.2
kg/ha/d for each 10.0 kg/ha/d increase in the manuring rate. Planktophagic fishes accounted for about
75% of this response. The conversion of manure to fish biomass was in the ratio of 8.3 kg dry manure:
1 kg wet fish weight. The contribution of primary productivity to fish yields was estimated in control
ponds to which nothing was introduced except inorganic nitrogen and phosphorus equivalent to the
amounts introduced as manure in the
Potential Health Hazards of Fish from Manured Ponds
The introduction of a fishpond as a farm subsystem should not pose any unacceptable risks to
public health. There is a possibility that livestock manured ponds may present health problems for
humans because some diseases of animals are transmissible to human beings. Although there are few
data in the literature on disease transfer through the use of manure as a pond fertilizer, it does appear
that the risk of disease transmission via fish grown in such ponds is low. Furthermore, such fish are
nutritionally and economically beneficial for farmers and consumers. Fish are not susceptible to most
infections of warm blooded animals (livestock and man); they are healthy and demonstrate good
growth in well managed manured ponds. The main danger lies in the passive transfer of diseasecausing microorganisms like Salmonella. However, there is a rapid decrease and weakening of
microorganisms in manured ponds in the tropics, probably due to high temperature, pH, and dissolved
oxygen. As a final safeguard, fish raised in manured ponds should be washed and cooked well prior to
consumption.
192
The construction of fishponds may provide breeding sites for disease-transmitting insects,
particularly mosquitoes that may transmit malaria. However, mosquito breeding in ponds can be
largely controlled by good design and management, in particular by preventing vegetation either
hanging into or emerging through the surface of the pond. On the other hand, the fish themselves may
aid mosquito control by the consumption of larvae.
ACKNOWLEDGES
The author thanks deeply to Nassa Caritas staff for their hospitality and good examples in the
caring of nature and the poor of the poorest people and those needed in many rural areas of the
Philippines. He also pay gratitute to Caritas Austria as sending organisation and to EUAV programme
for givng him the opportunity and support to discover the fascinating mixed latino asian country about
what this book talks. Thanks.
193
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