CONSERVATION TILLAGE IN MEXICO AND LATIN AMERICA: AN OVERVIEW
Ramón Claverán Alonso
INIFAP - CENAPROS
Agriculture is the most peaceful activity but it is subject to internal and
periodical revolutions that change and give a new life to it. Many of those changes
should have presented along history. The first outstanding recent change was that of
the nineteenth century with the industrial revolution that caused big changes in the
agriculture, but the changes that occurred during the twentieth century, especially
those during the second half of the century are the most outstanding. A remarkable
breaking point was the so called “Green Revolution” during the 60’s that summarized
technologies generated by research in practical application formulas that definitively
increased productivity substantially wherever environmental conditions were
appropriate, and necessary resources were available.
The green revolution was focused mainly on productivity, but less than decade
later the world reaction against it started being noticeable, being the world worried by
the natural resources preservation, that the green revolution had not taken into
account. The sustainable agriculture concept started being known in many countries
as a conciliatory and permanent solution between productivity and natural resources
conservation, mainly soil, water, and biota. The first forceful step to access to
sustainable agriculture is to practice the conservation tillage in some different ways
such as minimal up to zero or no-tillage at all. No matter what form of conservation
tillage is applied, it is indispensable to cover the soil surface with part of the prior crop
residues to approximate to the natural process.
The United States of America was the site of origin of the conservation tillage
as well as the country with the largest surface under that agricultural system,
followed by several American Continent countries. Within this world region there is 96
per cent of the world surface under conservation tillage (Derpsch, 1999). The process
of change from either conventional or traditional agriculture to conservation tillage is
not simple. In the case of Mexico, whose macro-scenario and background will be
described to explain the present situation of the country that is without any doubt
backwards, but not atypical for most of Latin American countries in relationship to
conservation tillage application.
SCENARIO
Mexico has a 194 million hectare surface (near an one third of the United
States surface). Near a 30 million hectare surface is cultivated of which only 20
million (near 10 per cent of the total surface) is harvested annually . The country
presents a large altitude variations due to two mountain chains that run along the
country, and merge to form a third mountain chain in Southern Mexico. The above
mentioned topographic relief combined with the latitude differences originate an
ample climatic system that goes from extremely arid with annual mean rainfall of less
than 200 mm, to tropical humid climates with annual mean rainfall over 2,000 mm.
There have been identified 28 climate types within a complex mosaic in which in more
that 50 per cent semiarid and arid climates predominate unfortunately (Medina et al.,
1998).
The geologic origin, topographic relief, and climate have originated a great soil
variability in Mexico where there are present 25 of the 28 soil units proposed by
FAO/UNESCO/ISRIC. Most abundant soils in Mexico are: Leptosols, Regosols, and
Calcisols (INEGI, 1998).
There are 37 hydrological regions in the country, and delimited 314
watersheds. Mexico receives near 475 cubic kilometers of water of which 182
thousand million cubic meters are stored in 2,100 reservoirs.
Exclusively for practical purposes Mexico was divided in four macro regions: arid and
semiarid (with 150 to 500 mm annual rainfall) 52 per cent of the country surface;
temperate (with 600 to 900 mm) 13 per cent of the country surface in which most of
the hilly areas are located; dry tropics (900 to 1,200 mm) 27 per cent of the country
surface; and humid tropics (over 1,200 mm) 8 per cent of the country surface. Of
course this is not a scientific classification, but it gives a general idea on the macro
regions of the country.
During the twentieth century, the human population increased too much in
Mexico; during the first half of the century the population doubled from 10 to 20 million
inhabitants, but in the second half, it increased from 20 to almost 100 million
inhabitants (400 per cent) which follows somehow the world trend. Besides that
important and worrying demographic growth, the population moved to the cities.
Mexican population was predominately rural (80 per cent) up to the middle of the
century, but nowadays 80 per cent of the population is urban. Numbers were
practically reversed. Migration from the fields to the cities is a phenomenon extended
to all Latin America. Migration of especially rural population to other countries is
another phenomenon that has been growing during the last half of the century
(INEGI, 1991).
MEXICAN AGRICULTURE
The Mexican agriculture was originated by the merge of two cultures. The base
was the Mesoamerican native agriculture that was 5,000 to 9,000 years old, and
among other developments it had domesticated maize (Fussell, 1992). Over that
really conservation agriculture, since they sowed directly, and never left the soil bare.
Even the “cutting-stubbing-burning” system was not damaging since the soil rest
periods were long enough to permit soil rehabilitation. Over that agriculture the
European agricultural systems were superposed , mainly those from the
Mediterranean that brought to the American Continent new crops and tools, as well
as equipment to develop another type of agricultural production. Maybe the most
outstanding issue was to introduce a new source of energy from animals, horses and
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mules, and bovine to the systems, that was unknown in the continent. That energy
pulled an Egyptian type plough that moved the soil, but it did not invert it, doing a
chisel type work.
Both cultures integration was done step wise and originated varied indigenous
systems adapted to different environments of the country. The agriculture that
depends of the human energy has not disappeared completely due mainly to the
troubles that present the agricultural use of extremely steep slopes, very abundant in
Mexico or due to the farmers’ lack of resources to buy or rent animals even if they
have flat soils (Cruz, 1997).
During the nineteenth century there were introduced some technological
insumes from other countries, but they did not produce any important change on
agricultural systems. The real evolution of the Mexican agriculture started during the
twentieth century, especially during the last 50 years. The mould-board plough that
inverts the soil profile invented in Holland and redesigned and mass commercialized
in the United States by John Deere since the middle nineteenth century was made
popular in Mexico almost a hundred years later, but nowadays the tendency is to
eliminate it completely from agriculture for the benefit of the soil.
Transformation of agriculture in Mexico was accelerated since the mid
twentieth century, at the beginning of the Second World War that was the start of the
present globalization process. Maize and wheat genetic improvement, chemical
fertilizer and pesticide mass application culminated with spectacular technological
advances, and the whole package was denominated “green revolution” and was
applied very successfully to production only where the environmental and
socioeconomic conditions were favorable. The next step was to popularize green
revolution formulas to all the country agricultural systems. Of course it was not
possible, but it was possible to incorporate to almost any agricultural system some
single elements of the green revolution technological catalogue such as: improved
seeds, chemical fertilization, insect pest control, and other that could have been
applied separately in many cases. There is an enormous diversity of number and
intensity of how those elements concur to present production systems. The new trend
to the conservation agriculture that was initiated during the 70’s followed and keeps
advancing step wise in the Mexican agriculture will be described in this paper.
The present situation of Mexican agriculture is defined by a number of factors.
Since it is not possible to use all of them to classify production units, the source of
energy used to do most activities required by crops especially in the soil is used to do
it. Data of Table 1 give a general idea of the rural socioeconomic development, farm
capital accumulation, as well as the difficulty to develop agriculture on marginal land
steep slopes that have to be hand worked. Most of those lands are appropriate for
forestry activities, water storage or other uses.
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Table 1. Classification of agricultural producers by the energy source used
(INEGI, 1991)
Energy source used
Number of producers (thousands)
Human energy only
Animal energy
Animal energy and tractors
Completely mechanized
Total
1,200
1,200
400
685
3,485
THE DETERIORATION PROBLEM
Along demographic growth and agriculture modern development natural
resources deterioration has become a growing and worrying problem during the last
half century. Mass y García Oliva (1990) analyzed the reports of five authors that had
estimated the soil accelerated erosion affected surface in Mexico, and the average of
those estimations was over 80 per cent. Near 535 million tons of soil are lost annually
(SEMARNAP, 1997); 69 per cent of those sediments goes to the sea, and 31 per cent
is deposited on rivers, lakes, reservoirs, and small water deposits. This silting up is a
double problem since it is necessary to clean all water stores, and that labor is
difficult. Inappropriate management of the three basic activities: deforestation without
replanting balance, over grazing, as well as conventional, and traditional as cuttingstubbing-burning agriculture that deteriorates natural resources at different degrees.
In zones with steep slopes as the Tuxtlas region, Veracruz, to produce a
kilogram of maize has an ecological cost of 27 kilograms of soil. It has been
estimated that more soil has been lost during the last 40 years than that lost during
400 years of the history of the country (Mason, 1984 in Maas y Garcia-Oliva, 1990).
There have been estimated agricultural land annual losses from 250,000 to 300,00
hectare. If that trend is not modified a major part of the agricultural land will be lost for
the twenty first century.
Besides the soil loss, the nutrient available for plants loss due to runoff and
percolation to deep water reservoirs is also very important, since they produce a
double damage: first the most of applied fertilizer loss, and second the toxic
substances such as nitrates accumulation in the water. Nitrogen is the most
important element for both types of damage; it is the nutrient applied to maize crop
that consumes more energy to be produced; since even in conventional tillage,
nitrogen fertilizer production consumes more energy than that from fossil fuels used
for labor. In the Bajio region, one of the most important agricultural regions of Mexico,
only a third part of the nitrogen applied to wheat crops is profited by the plant
(Grageda, 1999). In the Patzcuaro, Michoacan watershed, a nitrogen loss by maize
crop cycle is 2.5 times higher with conventional tillage than with no-till (Velasquez et
al., 1997). Nutrient loss from the soil is an area under research in which more
information is required to measure more precisely the nutrient loss problem, but it is
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even more urgent to stop the loss process, for which conservation tillage has
demonstrated to be the solution.
CONSERVATION TILLAGE IN MEXICO
Background
As above mentioned, the enthusiasm for the green revolution lasted for less
than a decade, a series of factors such as the oil crisis that occurred in the United
States in the 70’s, the droughts in Africa, pollution, and the high soil loss indexes all
over the world created the need for change in agriculture that started precisely in the
United States.
One of the first approaches in Mexico with the new crop system took place at
the end of the seventy’s when the International Center for Maize and Wheat
Improvement (CIMMYT) started a training program and invited a group of
researchers and technicians from FIRA (second floor financing and development
institution) and from National Institute of Forestry, Agricultural, and Animal
Production Research (INIFAP) to a trip through different agricultural regions that had
adopted the conservation tillage in the United States. When they were back to Mexico
both institutions started to develop conservation tillage activities within their
respective fields: demonstration and promotion in FIRA, and research in INIFAP.
Since then FIRA started a permanent training program on conservation tillage,
built training centers, and established an extensive net of demonstration plots,
conferences, international congresses, producers’ organizations, and of utmost
importance promoting and providing less expensive advanced and capitalization
credits to farmers through first floor banks to encourage the conservation tillage
adoption in the country (Gonzalez, 1990).
Research
Research on conservation tillage at INIFAP was initiated during the 50’s when
some no-tillage experiments were established even if the soil was not covered with
residues. Results obtained were not outstanding, and that aspect of research was
abandoned, and only some isolated essays were done later. Research on
conservation tillage was reinitiated after an observation trip sponsored by CIMMYT.
Several experimental plots were established in different locations in the country, but
unfortunately that activity went down. At the early 90’s, INIFAP’s Central and Central
Pacific regions established a coordinated and more aggressive research program on
conservation tillage. In 1996, INIFAP created the National Research Center for
Sustainable Production (CENAPROS) responsible for coordinating research activities
on conservation tillage done in the eight INIFAP’s regional research centers, where
near 55 researchers participate directly in research within a national conservation
tillage program. The first report of that program with results obtained by INIFAP and
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other related by affinity institutions was published in 1997 (INIFAP-CENAPROS,
1997).
Other institutions have also developed research and conservation technology
transference programs, some of them are educational. Colegio de Postgraduados
(Graduate College) is the most active institution in this field, a number of thesis to
obtain Master’s and Ph. D.degrees have been done on conservation agriculture
emphasizing on soil characteristics and their relationships. CIMMYT has worked
mainly in tropical regions for longer than 10 years: La Fraylesca y Motozintla,
Chiapas (Van Nieuwkoop, 1994), and Los Tuxtlas, Veracruz (Erenstein y Cadena,
1997; Buckles y Erenstein, 1996; Soule, 1997) and Ciudad Guzman, Jalisco (Scopel,
1997). Also some non governmental institutions (NGI) are participating within the
research-technology transference field. An example is the network financed and
consolidated by the Rockefeller Foundation that operates in tropical regions mainly, in
coordination with universities, research institutions, state governments, and other
NGI. One of their most important programs is being developed in southern Sinaloa
where work is being done on agricultural-forestry-pastoral natural resources
management with conservation tillage for forage production. in coordination with
INIFAP, and Chapingo Agricultural Autonomous University (UAACH) (Herrera y
Palacios, 1996). That zone is one of the pioneer regions for that type of forage
production.
Research done up to date has given priority to crucial aspects of conservation
tillage. The most important questions at the beginning were to define the most
efficient conservation tillage type, either minimal or zero tillage, and when was
necessary to recommend ridge tillage, in comparison to conventional tillage. Other
question was what was the minimal prior crop residue quantity o be left on the soil,
due to the high importance of this issue in Mexico. A third question was the sowing
machine type that presented efficiency and low price characteristics. It was also
indispensable to learn about the behavior of those conservation tillage practices
under irrigation and rainfed conditions.
Experimental results showed in first place that there were significant
advantages of zero tillage over either conventional or minimal tillage. It was detected
that when minimal tillage was applied on steep slopes more erosion than that
produced using conventional tillage. Under slope and Andosols conditions there were
found differences of 400 per cent more erosion with conventional tillage in
comparison o zero tillage in the first years (Tiscareño et al., 1997). In cultivated
lands on steeper slopes in southern Veracruz it was found that to produce a kilogram
of maize with conventional tillage caused a 27 kilogram of soil loss while under zero
tillage the loss was reduced to less than a kilogram of soil as four year average
(Uribe, 1998) . Over a 100 experiments done by the national program during five
years showed that zero tillage reduces the erosion rate in near 80 per cent in maize
crop, and in near 95 per cent in wheat crop in comparison to conventional tillage.
Along time, the use of zero tillage tends to increase even more the soil protection
(Osuna, 1997; Velasquez, 1997).
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It was found in Mexico and other countries that if the third part of prior crop
residue is left on the soil the protection against erosion is good enough in temperate
climate environments (Velasquez, et al., 1997). In tropical climates that is not enough
since a larger quantity of residues is required due to the high decomposition rate of
organic matter (Van Nieuwkoop et al., 1994; Erenstein, 1999). Along years, the
research program has obtained enough experience on the most important crop
residues, maize stubble and wheat straw.
Agricultural machinery was a very important limiting factor for zero tillage
initiation during the first years, since the available sowing machines were imported
and too expensive for most farmers. Afterwards, INIFAP (Del Toro, 1997; Campos,
1996, 1997, 1999) and UAACH (Gaytan et al., 1996), and other institutions have
designed some functional equipment for mechanical and animal traction. Also 12
small private companies, at least, have designed, produced locally, and introduced to
the market sowing machines, and even some produce precision machines for sowing
directly (Dobladense as an example). On the other hand, big companies such as
John Deere and New Holland have started making sowing machines for small and
medium size producers in Mexico.
It was found through research that:
1) there was not found difference of behavior of improved maize genotypes
generated either by INIFAP or by private companies, when sown under
either conventional or zero tillage;
2) rainfed maize productivity under conservation tillage increased a five year
average from 10 to 15 per cent since the first years in temperate climate
regions, but in tropical areas production has increased up to 32 per cent in
comparison to that obtained with conventional tillage(Van Nieuwkoop et al.,
1994);
3) rainfed maize and irrigated wheat production costs were reduced 25 to 30
per cent in comparison to those with conventional tillage;
4) average soil humidity content was 20 per cent higher with conservation
tillage than that with conventional tillage. It means an insurance in rainfed
agriculture.
Main constraints for conservation tillage adoption
Some barriers and barrier combinations have hindered the extensive diffusion
of conservation tillage in the fields:
1) five centuries old agricultural tradition has created a social attitude that
raises difficulties to change from conventional to conservation tillage,
particularly among elder producers;
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2) it is not easy to convince producers to leave stubble or straw on the soil
since: a) most producers use crop residues to feed animals during dry
season; b) some of them sell crop residues since they are a valuable
commodity in the market; c) some burn them to “clean” the land. There is
also a variant of this fact, the “cutting-stubbing-burning” system used in
southeast Mexico;
3) there are not yet enough technical advisors to provide enough quantity and
good quality technical assistance, and training to farmers. Bad experiences
with conservation tillage due to low quality technical assistance or lack of it
in a region make difficult its adoption;
4) rural enterprises’ capitalization degree is low and their access to credit not
easy especially for small agricultural producers (Van Nieuwkoop, 1994);
5) herbicide cost in Mexico is far higher than in other countries; as an
example, a litter of Faena (Round up) is ten times more expensive in
Mexico than in Argentina;
6) in the case of farmers that use human energy exclusively (1’200,000) to
produce maize and beans the first condition for adopting conservation
tillage is already satisfied, since they do not invert the soil profile, but do not
leave prior crop residues on the soil since most producers in the tropics
use the “cutting-stubbing-burning” system and the soil rests bare. Those
who do not do that practice are usually under those circumstances
described in paragraph 2) of this section.
PRESENT SITUATION
1)
Mexico has adhered international agreements for encouraging the use
of conservation tillage, signed the Rio de Janeiro Document, in which
Agenda 21 refers to conservation tillage among other methods to
conserve soil and water. Also, the Mexican Senator Chamber ratified the
International Convention for Fighting Against Desertification that also
involves it, as well as international networks, and associations for the
same purpose;
2)
FIRA has estimated a near 650 thousand hectare surface under
conservation tillage in Mexico (Ochoa, 1999). That surface represents
near 3.25 per cent of the land harvested in spring-summer and fallwinter cycles. Surface under conservation tillage is concentrated in the
central-west Mexico 79.9%, in the southern region 10%, in the northern
zone 1%, and only 0.2 in the north eastern region. About crops, maize is
the most important with near 57% of the surface, followed by sorghum
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37.8%, wheat 8.4 %, and other crops 0.8% among which there are
some vegetables as broccoli.
3)
Mexican federal and state governments encourage the use of
conservation tillage. The Agriculture, Animal Production, and Rural
Development Secretariat (SAGAR) hired 8 thousand technicians all
over the country. Half of them to advice how to increase productivity,
and the rest of them for rural programs development. During 1999, 202
courses on conservation tillage and similar practices were taught to
5,827 technicians to help the Sustainable Agriculture and Productive
Conversion. Alliance for the Field Program subsidizes 20 per cent of the
conservation tillage sowing machine and tractor buying price to
producers, and machinery reparation;
4)
in Mexico there are both, structure and human resources to develop
research programs both in INIFAP and in the universities. Obviously,
effort integration is lacking. For technology transference, there are those
elements before mentioned for Alliance for the Field Program. FIRA is
developing a permanent program training near 300 technicians and
producers yearly in its specialized center, besides the other aspects
FIRA works on to encourage conservation tillage use, of which the most
important is the financing discount to establish conservation tillage and
machinery buying;
5)
the knowledge and experiences on conservation tillage accumulated
in Mexico are good enough to be applied to main staple crops. It is still
needed to do research on cause-effect relationships to make processes
more efficient as: microbiology-organic matter, carbon-nitrogen, waterclimate relationship, root pests, and other. Also it is necessary to do
more research on some practical problems to solve them as those that
present in red tropical soils where the conservation tillage has not been
successful (Van Nieuwkoop, 1994);
6)
along the improvement of the knowledge on conservation tillage, it is
urgent to step on the next phase of the conservation agriculture, which
is to improve soil fertility using combinations of conservation tillage with
green manure crops, crop association and rotation of crops as they are
doing in Brazil. Right now, we are wasting that opportunity that means
soil improvement, and welfare for producers.
CONSERVATION TILLAGE IN LATIN AMERICA
As above mentioned, the largest surface under conservation tillage after that of
the United States’ is in South America. Conservation tillage has extended the most in
Brazil, Argentina, and Paraguay. In other countries it is still incipient (less than 100
thousand hectares) or even extremely low in relationship to the total agricultural
9
surface as in the case of Mexico above described. There are two country cases to
mention.
The case of Costa Rica is unique and merits to be mentioned. Practically the
country has an extremely small surface under conservation tillage (less than 100
thousand hectares), but it has consciously structured and approved an extremely
advanced legislation on conservation tillage to integrate it to its agriculture as they are
initiating now.
El Salvador, in despite of the problems due to the internal war that suffered
recently, is one of the conservation tillage pioneers in Latin America, and
demonstrated that conservation and productivity might be successfully associate
within a productive system. A program was started in 1970 to incorporate
conservation tillage to the traditional maize-sorghum association that was manually
sown in the Guaymango region with a near 5,000 hectare surface with very steep (40
to 90 percent) slopes. Small producers keep working manually mainly, and using a
little animal traction. Before adopting conservation tillage they had already adopted
hybrid seeds and chemical nitrogen and phosphorous fertilizers. They had also
stopped burning crop residues to leave part of them on the soil. During the following
16 years maize production increased form 0.7 to 3.23 ton/ha and that of sorghum
from 0.6 to 2.1 ton/ha, and regional producers obtained also the rest of soil
conservation and improvement benefits (Sain y Barreto, 1996; Erenstein, 1999).
Unfortunately, the conservation tillage has not extended as much as it was expected
there is only a 2,000 hectare surface under conservation tillage in the country.
Brazil is the most advanced and largest conservation tillage adoption case in
Latin America, and it is a good example for the world as a whole. Favorable
circumstances for the adoption have been: versatility of ecological environments
where the conservation tillage is used, size variety of farms from small to large
producers, the cleverly made machinery they have designed for either animal or
mechanical energy, the ample catalogue of developed imaginative technologies
applied extensively. The surface covered with conservation tillage is near 12 million
hectares, that is near the third part of the total land cultivated in the country. That
surface has been increasing more than a million hectares yearly during the last four
years (Derpsch, 1999).
The use of conservation tillage in Brazil started in Parana and Rio Grande do
Sul during the 70’s, after some outstanding agriculturists visited the University of
Kentucky and who became interested in the change. At the beginning they had
troubles due to the lack of direct sowing machines and they had to import them, but
they solved the problem adapting the conventional sowing machines they already
had to direct sowing. Another important problem was the herbicide scarcity and high
price. State research participated since the mid seventy’s in coordination with
commercial companies and international agencies. Parana became the new
technology diffusion center for Southern Brazil. Later, conservation tillage was
diffused to other regions among which there were the maize and soja beans producer
large extensions of Central West Brazil (Da Veiga, 1997; Derpsch, 1998).
10
One of the most important characteristics of the conservation tillage adoption in
Brazil is that it surpassed its limits to complement it with other practices such as:
green manure, and crop association and rotation. They use a number of legumes to
increase the soil available nitrogen content, but also cereals as very short cycle millet,
and black oats very popular in Southern Brazil. Crop rotation alternating generally
cereals and legumes was the most practical remedy to solve soil problems caused by
monocrop (Da Veiga, 1997).
Another very important focus of conservation tillage in Brazil has been the
integration of agricultural, animal production and forestry systems within the
watershed concept better than county limits. This has made easier the development
of long reach programs financed nationally and internationally (CEPA/SC, 1999).
Within the above mentioned structure (and practically in any other structure) the
programs have obtained success due to the producers’ collaboration who have
contributed with work and other resources, as well as the dedication of managers,
technicians, researchers, and service providers, who have organized very efficient
teams.
Argentina, second conservation tillage Latin American adopter country,
initiated its research and practical conservation tillage implementation by producers
since 1974. For that time, at the beginning, the bottle neck was also either lack,
scarcity, or high price of herbicides and sowing machines. Agricultural producers had
reached a high organization level with conventional tillage and nowadays they have
reached an excellent organization level on conservation tillage matter. The surface
under conservation tillage in Argentina increased from 25 thousand in 1988 to 7
million hectares to date. The initial panorama on machinery and herbicides has much
changed in Argentina, there are 30 industries that produce direct sowing machines
and herbicides are produced in the country (Derpsch, 1998).
Although in both Brazil and Argentina conservation tillage is widely used, it is
necessary to remark some differences: there are not extremely small farms, extensive
and well organized and rural enterprises predominate in Argentina, and agriculture
depends on mechanical energy mainly. Conservation tillage have not been integrated
neither to green manure nor to crop rotations and watershed management concept
as in Brazil.
Paraguay is an exceptional case due to the speed of change from
conventional to conservation tillage in relationship to the agricultural surface of the
country, although small farms predominate, and there occur most of unfavorable
characteristics of tropical countries. First attempts were made during early 80’s, but
the failed due to machinery low quality and lack of herbicides. Later, the government
associated to Japan’s JICA could start a conservation tillage adoption program. In
1992, there was a surface of only 20 thousand hectares under conservation tillage. In
1993, a government and Germany GTZ program started. In 1998 there were 80,000
hectares under conservation tillage, most of it cultivated with soja beans. This
11
program supassed all its goals, and conservation tillage covers more than 50 per
cent of the country (Derpsch, 1998; Derpsch, 1999). On the other hand, Latin
America is the region in the world that has most researchers, and technicians
networks, as RELACO, and CAAPAS. This last one is a federation of Latin American
sustainable agriculture associations that has such a high prestige, that some other
associations from other world regions have joined.
BIBLIOGRAPHY
Buckles, D. y O. Erenstein .1996. Intensificación de los sistemas de cultivos basados
en el maíz en la sierra de Santa Martha, Veracruz. NRG 96-07 Es. México, D.
F.: CIMMYT. 62 p.
Campos, S.M. 1996. Desarrollo de una sembradora de labranza de conservación
para dosificar mecánicamente. IX Reunión Científica y Tecnológica Forestal y
Agropecuaria de Veracruz. INIFAP- CIRGOC. 124-131.
Campos, S. M. 1997. Force measurement and recording data analysis system for
tillage tools. Agriculture Mechanization for Asis, Africa, And America 28:19-25.
Campos, S. M. 1999. Desarrollo de equipos de siembra para labranza de
conservación acoplados a equipos multiusos de tracción animal
IX Congreso Nacional de Ingeniería Agrícola 80-87.
CEPA/SC 1999. Avaliacao do projeto de microbacias. Relatorio de avaliacao final.
Instituto CEPA/SC. 37 p.
Cruz, L. A. 1997 ..Y sigue la yunta andando. Univ. Aut. Chapingo 173 p.
Da Veiga, M 1997 Plantio direto no Brasil Mem. RELACO IV México 123-137.
Del Toro, J.A.M. 1997. Sembradora INIFAP para labranza de conservación. Avances
de investigación en labranza de conservación. INIFAP-CENAPROS. Libro
Técnico No. 1. pp. 181-197.
Derpsch, R. 1999. Expansión mundial de la siembra directa y avances tenológicos.
Memoria de la V Reunión RELACO. Florianópolis, Brasil. In press (CD).
Derspch, R. 1998. Historical review of no-tillage cultivation of crops.
Conservation tillage for sustainable agriculture. International
Workshop. Harare, Zimbabwe. 205-218 p.
Erenstein, O. C.A. y P.I. Cadena 1997. La adopción de labranza de conservación en
un sistema de cultivo en ladera en Motozintla, Chiapas. NRG 97-01
Es. Mexico, D.F.: CIMMYT. 54 p.
12
Erenstein, O.C.A. 1999. The economics of soil conservation in developing countries.
The case of crop residue mulching. Thesis. Wageningen University. 301 p.
FAO 1999. Información personal de la Delegación FAO en El Salvador.
Fussell, B. 1992 The story of corn. Alfred A. Knoff 356 p.
Gaytán J.G.R., A.J. Avila y J.L. Grajales 1999a. Adaptación y evaluación agrotécnica
de una sembradora para condiciones de labranza de conservación
sobre un monocultor. Memoria del Simposio Nacional sobre Labranza
de Conservación. Montecillos, Mex. Resumen 79-80.
Gaytán J.G.R., A.J. Avila y J.L. Grajales 1999b. Sembradora fertilizadora tipo unitario
de tracción animal para condiciones de labranza de conservación.
Memoria de Simposio Nacional sobre Labranza de Conservación.
Montecillos, Mex. Resumen. 81-82
González, L.L.R. 1990. Labranza de conservación una alternativa para
aumentar la producción y productividad del agro mexicano. FIRA
Boletín Informativo 222, 44 p.
INEGI. 1991. VII Censo Agrícola-Ganadero. INEGI. Aguascalientes, Ags., México.
2 volumes. (857 p., and 796 p.)
INEGI, 1998. Estadísticas del medio ambiente. México 1997. INEGI,
SEMARNAP. 461 p.
INIFAP-CENAPROS, 1997. Avances de Investigación en labranza de conservación.
INIFAP-CENAPROS. Libro Técnico No. 1. 288 p.
Leite, H.M.C. 1997. Efeitos do plantio direto sobre o medio ambiente. O medio
ambiente o plantio direto. Associacao de Plantio Directo no Cerrado. 5766.
López, H.A. y O.V. Palacios 1996. Desarrollo sostenible de los agroecosistemas del
Sur de Sinaloa. Fund. Rockefeller, INIFAP, UACH. Informe II 1994-95.
191 p.
Mass, J.M.M. y F. García-Oliva 1990. La conservación de suelos en zonas
tropicales: el caso de México. Ciencia y Desarrollo 90: 21 - 36.
Medina G.G., J. A. C. Ruiz, y R. A. P. Martinez 1998 Los climas de México SAGAR,
INIFAP, CIRPAC 101p.
Ochoa,G. 1999. (FIRA) Comunicación personal.
13
Sain E.G. and H.J. Barreto 1996 The adoption of soil conservation technology in El
Salvador: Linking productivity and conservation. J. Soil and Water Cons.
51: 313-321.
Scopel, E. (Ed.) 1997. Memoria del taller de transferencia de labranza de
conservación para maíz de temporal en el Estado de Jalisco.
México, D.F.: CIMMYT, INIFAP, CIRAD, SDR. 83 p.
SEMARNAP, 1997. http://www.semarnap.gob.mx
Soule, M.J. 1997. Farmer assesment of velvetbean as a green manure in
Veracruz, Mexico: Experimentation and expected profits. NRG
paper 97-02. Mexico, D.F.: CIMMYT 21 p.
Tiscareño L. M. Gallardo y M. Velázquez 1997 Impacto de los sistemas de
Labranza en las laderas. Avances de Investigación en labranza de
Conservación I. INIFAP-CENAPROS. pp. 107-122.
Uribe S. 1998. Tecnologías prosostenibles de manejo de suelos tropicales en el sur
de Veracruz. Memoria de la XII Reunión Científica y Tecnológica, Forestal y
Agropecuaria INIFAP-CIRGOC. 93-100.
Van Nieuwkoop, M., W.B. Walter, A. M. Zamarripa, R.C. de la Piedra, F.U.C. Cruz,
R.G. Camas, J.L. Martínez 1994. La adopción de tecnologías de labranza de
conservación. La Fraylesca, Chiapas. CIMMYT-INIFAP. 93 p.
Velasquez, M.A.V., M.L.Tiscareño, R.A. Claverán y M.V. Gallardo 1997. Erosión
y productividad bajo labranza de conservación I. Avances de
investigación en suelos de ando de Michoacán. INIFAPCENAPROS. Folleto Técnico N° 1. 34 p.
Webb, W.P. 1931. The great plains. Grosset & Dunlap. 525 p.
14