Module IV, Section C
Horticulture Crops in the agro-ecosystem
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Projected Outcomes
Background / Lessons
o Introduction
o The Ground Beneath Our Feet
o Ecological question 1: What are the nutrient and water flows in the system?
o Ecological question 2: What are the sources and sinks of pollutants in the
system?
o Ecological question 3: What are the interactions of living organisms in the
system?
o Ecological question 4: What are the energy flows in the system?
 Activities
Projected outcomes:
1. Students will begin to apply ecological analysis to vegetable and fruit production
systems.
2. Students will learn about some key agro-ecological management practices,
including soil and fertility management, crop rotation, and pest management.
3. Students will gain an appreciation of the complexity and variety of the
agroecology of horticultural crops.
Background / Lessons
Introduction
Like natural ecosystems, agro-ecosystems are characterized by nutrient flows and cycles,
energy flows, and the interactions of living organisms with each other and the physical
environment. However, agro-ecosystems differ from natural ecosystems in two key
ways:
 First, we expect them to export particular biological goods for our use.
 Second, we deliberately manipulate them to get them to produce those goods in
abundance.
These two special qualities of agro-ecosystems in turn affect their key ecological
processes. Sustainable agriculture seeks to take advantage of ecosystem processes by
designing an agricultural system that works with them rather than against them to achieve
its production goals.
This section begins with a quick look at the role of the soil in the agro-ecosystem and
then encourages students to think about the ecology of horticultural production by posing
four ecological questions.
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2)
3)
4)
What are the nutrient and water flows in the system?
What are the sources and sinks of pollutants in the system?
What are the interactions of living organisms in the system?
What are the energy flows in the system?
Horticultural crops vary widely in their ecological characteristics, from row-cropped
annual vegetables to fruit trees that may be productive for more than 30 years. Moreover,
while some fruit and vegetable farms specialize in producing one or two crops, others
produce dozens of different kinds of plants. This unit will provide some indication of
the variety of sustainable horticultural systems in Iowa and Wisconsin, but it cannot
cover it all. Classes are encouraged to apply the four agro-ecological questions to crops
grown in their areas.
The Ground Beneath Our Feet
"The nation that destroys its soil, destroys itself." - Franklin Delano Roosevelt
Essentially, all life depends upon the soil .... There can be no life without soil and no
soil without life; they have evolved together." - Charles E. Kellogg, USDA Yearbook
of Agriculture, 1938
See http://soils.usda.gov/education/resources/k_12/quotes/ for more soils quotes
Every farmer knows that soils are important. But different farmers (and scientists) think
about soils in different ways.
One way to look at soils is as a physical medium. It needs to serve a variety of
mechanical functions: provide a substrate for plant roots to grow in, allow water to drain
so plant roots have access to oxygen, but hold on to enough water that roots have access
to water. The soil is also where plant nutrients are stored, transferred to roots, and
sometimes lost.
Many sustainable farmers think about soils as a living system. They value the
mechanical functions of soil, but they look beyond those properties to biological and
ecological services. These farmers seek to build and maintain good soil health, rather
than simply avoiding damaging the physical structure of the soil.
Activity 1: Trial by Water
Our understanding of soil biology is still quite rudimentary, but we are learning more and
more about how the multitude of living organisms in the soil affect soil quality and
processes and about how our actions in turn affect the life of the soil.
Key groups of soil organisms include:
Bacteria (single-celled organisms that are neither plants nor animals)
Fungi (neither plants nor animals, typically grow in long chains of cells called hyphae)
Protozoa (single-celled animals such as amoebae)
Nematodes (tiny non-segmented worms)
Arthropods (invertebrates such as insects, spiders, millipedes, etc.)
Earthworms
(Plant roots)
Each of these groups contains a wide variety of species, and the different species do very
different things. For example, one gram of soil may contain 11,000 different species of
bacteria. Some bacteria help decompose organic matter, some fix nitrogen, some prey on
living organisms causing disease, and a few bacteria photosynthesize.
Together, soil organisms perform critical ecological functions such as decomposing
organic matter, changing soil structure, moving, stabilizing, and transforming nutrients,
altering chemicals such as pesticides, and eating or helping each other.
Soil ecology introduction powerpoint
As you look at the four ecological questions below, keep the role of the soil and of soil
organisms in mind.
What are the nutrient and water flows in the system?
Several factors influence the nutrient and water flows in horticultural production.
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All plants require nutrients to grow. Because they take nutrients away from a
site when they harvest crops, farmers have to replace those nutrients to keep
that land productive.
However, different crops have different nutrient needs. For example, spinach
and sweet corn require lots of nitrogen to yield well, while beans, peas, and
many fruits do well with little added nitrogen but may have special water or
micronutrient requirements.
The growth habit of the crops is also important. A “crop” such as turfgrass,
with year-round ground-cover, requires different nutrient and water
management than for example tomatoes, which only grow in summer and are
generally surrounded by bare soil or possibly a non-living mulch.
Even within a crop type, different management approaches can have significant
impacts on nutrient and water flows.
Let’s take a look at nutrient and water impacts of two crops: sweet corn and cranberries.
Sweet corn
Nothing symbolizes the taste of summer quite like fresh sweet corn. Customers seek out
the varieties they like – super-sweet “Sugar Buns” or elegant white “Silver Queen.” But
most don’t think beyond appearance and flavor to how the corn was raised.
Sweet corn grows best with lots of sunshine, enough but not too much water, and lots of
nutrients in the soil, especially nitrogen. Because corn responds well to high fertility, it
can be tempting to add generous amounts of fertilizer. But excess nitrogen can leach into
groundwater, and phosphorus can run off into surface water, damaging aquatic
communities and drinking water supplies. (See http://ohioline.osu.edu/aexfact/0463.html or http://extension.missouri.edu/explore/envqual/wq0252.htm for a
summary of the N cycle in agronomic systems.) In addition, money spent on unneeded
fertilizer cuts into farm profits.
Farmers can use a variety of practices to reduce the need for purchased fertilizer in sweet
corn production:
 Recognize that sweet corn needs less N than grain corn, because it is harvested
earlier. N recommendations for grain corn on similar soils can be reduced by ??
percent without affecting sweet corn yields????
 Use realistic yield goals when calculating nutrient needs.
 Supply N through crop rotation. If the corn follows a good stand of alfalfa or
clover, it will need no supplemental nitrogen. If it follows soybeans, potatoes, or a
small grain, N applications can usually be reduced by about 30 to 40 lbs per acre.
Crop rotation also benefits sweet corn by reducing a number of key pests.
 Use a late spring soil nitrate test to measure available nitrogen already in the soil,
rather than assuming the crop will need all its nitrogen supplied by fertilizer
applications. (See “Nitrogen Fertilizer Recommendations for Corn in Iowa,” p. 2
http://www.extension.iastate.edu/Publications/PM1714.pdf , “Using the Late Spring
Nitrate Test to Reduce Nitrate Loss Within a Watershed”
http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=149
625, “The Presidedress Soil Nitrate Test” http://ipcm.wisc.edu/pubs/pdf/PSNT.pdf,
and “Nitrogen $ Rate of Return Calculator”
http://www.uwex.edu/ces/crops/NComparison.htm . Remember to adjust grain corn
recommendations downwards for sweet corn.)
 Side-dress N applications while the crop is growing and can use the nutrients right
away, rather than relying on fall or pre-plant applications. Fall N applications are
likely to leach significant amounts of N.
 Use composted (link to header below) manures to supply the phosphorus,
potassium, and part of the nitrogen needs of the corn.
 Plant a cover crop such as winter wheat or rye after harvest to prevent runoff and
leaching of nutrients.
 Use conservation tillage to minimize runoff and erosion .
Cranberries
Compared to most crops, cranberries require very little fertilizer, in part because as
perennial plants they do not have to grow new stems every year and can store nutrients
over the winter. The recommended rates are from 20 to 40 lbs of N and 20 to 45 lbs of
P2O5 per acre per year. Compare these guidelines to recommended rates of 80 to 150
lbs/acre N and 0 to 100 lbs/acre P2O5 per year for sweet corn and 40 to 100 lbs/acre N for
broccoli.
Moreover, unlike most crops, cranberry yields decline quickly when too much nitrogen
fertilizer is applied. So you might think that should make sustainable nutrient
management for cranberries easy. But it is not so simple. The way cranberries grow
provides some special challenges.
Cranberry plants are very picky about what kinds of nutrients they will take up. Whereas
most plants will take up nitrogen as ammonium and/or nitrate, cranberries only use
ammonium. And while most food crops grow in nearly neutral mineral soils, cranberries
grow in acid soils that are high in iron and aluminum. These special soil characteristics
change the behavior of phosphorus in the soil. On top of that, cranberry bogs are
regularly flooded to help with harvest and prevent frost damage and winter kill. This
flooding means that nutrients that are not held in the plant are more likely to run off to
surface waters (phosphorus) or leach to ground water (nitrogen).
These features mean that many of the usual tools for sustainable nutrient management
(use of manure, compost, legumes, and cover crops) don’t work for cranberry production.
The main approach that most cranberry growers have for improving the sustainability of
nutrient use is to fine tune the amount and timing of nutrients applied, using
 plant tissue testing to determine nutrient needs over the next 15 months,
 fertilizer selection to target P and N ratio and type to cranberry needs,
 careful monitoring of developmental stages and appearance of the plants to
determine optimum timing for fertilizer application, and
 accurate fertilizer delivery equipment.
These tools can help maximize the amount of fertilizer taken up by the plants and
minimize loss to surface or ground water. (See http://www.hort.wisc.edu/cran/, and
pages 24-25 of http://www.wiscran.org/WFPlanning/SamplePlan.pdf for more
information on fine-tuning nutrients for cranberry production.)
In recent years, with the growth of the organic market, some growers have started
producing cranberries organically. Organic growers rely on compost teas and fish-based
fertilizers to add nutrients. These materials do not provide the rapid release of plant
available N that synthetic ammonium and urea do, and the difference in nitrogen
availability is thought to be the main reason why organic cranberry yields are typically
much lower than conventional yields (see http://www.cias.wisc.edu/pdf/orgcran.pdf.).
Nevertheless, with good management and the price premium for organic products,
organic production is proving viable for a number of growers. Research, breeding, and
experimentation with organic management may improve yields considerably.
Because irrigation and flooding are such important practices in commercial cranberry
bogs, cranberry production also has special impacts on water cycling. Cranberry
growers store water in natural and artificial wetlands. On average, in Wisconsin each
acre of producing cranberry bog has about ten acres of support lands to store water.
Cranberry growers point out that these support lands provide habitat for a variety of
wetland plants and animals (http://www.wiscran.org/wetlands.htm) and that:
… growers now use sophisticated systems to conserve and recycle the large
amounts of water necessary for cranberry growing. All flooding and sprinkling
involves “borrowing” water from within the same system—it is just
temporarily moved from one area to another. Because cranberry vines and
berries absorb little water and the soil is saturated enough that little water
goes into the groundwater, the water is returned to its original location,
unchanged. The government considers cranberry growers’ use of water to be
predominantly “non-consumptive” because the water does not degrade in
quality or quantity.
(From “Wetlands & Cranberry Growing: Environmental Partners”by the
Wisconsin State Cranberry Growers Association
http://www.wiscran.org/crangrow.htm.)
. Critics note that cranberry irrigation and water storage for harvest can exacerbate the
impacts of drought on natural wetlands by withholding water that normally would
contribute to stream recharge. They also worry that water that has cycled through a
cranberry bog can pick up nutrients and pesticides that may then harm aquatic
communities.
Compost
Compost is one of the most important nutrient management tools for sustainable fruit,
vegetable, and flower growers. Composting is the controlled decomposition of biological
materials. (See The Art and Science of Composting.) (link to
http://www.cias.wisc.edu/archives/2002/03/01/the_art_and_science_of_composting/inde
x.php)
Compost offers several advantages:
 Nutrients tend to be stable and bound to organic matter, so they are less likely to run
off or leach than nutrients in raw manure or synthetic fertilizers.
 Compost has a mild “earthy” odor, unlike the unpleasant odor of manure.
 Compost acts as a soil amendment as well as a nutrient source, adding organic matter
and improving soil tilth.
 The composting process greatly reduces or eliminates pathogens that are harmful to
human health.
 Many types of compost contain far fewer viable weed seeds than regular manure.
 Compost can help suppress certain plant diseases.
Compost also offers some challenges:
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Up to half of the nitrogen contained in the material being composted is lost to the
atmosphere during the composting process. However in many trials, plants gown
with compost yield more than expected at low levels of soil N.
Compost can be highly variable, depending on the materials composted and on the
composting process. Growers need to be sure they are using the right type of
compost for their needs.
Compost is much bulkier and therefore harder to transport, store, and apply to large
areas than synthetic fertilizers.
Composting requires careful management, and depending on the composting system
chosen, may require expensive equipment.
Activity 2. Compost Recipes
Activity 3. Vermicomposting
What are the sources and sinks of pollutants in the system?
A sustainable system will minimize the amount of pollutants introduced into the
environment.
What is a pollutant? It is a chemical that is damaging to human health or the
environment.
Just as a weed is a “plant out of place,” so whether something is a pollutant depends in
part on context. For example, soil particles are a valuable resource in the crop field.
However, if those same soil particles are carried from the field to a stream or river by
erosion, they become sediment—a pollutant that can severely damage aquatic
communities.
Suggested activity: Resource or Pollutant
Thus, the source of many agricultural pollutants is deliberate application of inputs such
as fertilizers and pesticides. Another source is beneficial resources such as soil or
manure, which turn into pollutants when mismanaged and displaced. A sink is where the
pollutant winds up. Surface waters, including rivers, lakes, and the ocean, are a common
sink for agricultural pollutants.
The broad categories of pollutants in horticultural crops include:
 excess nutrients running off or leaching to surface and ground waters
 soil erosion degrading wetlands
 pesticides harming non-target organisms
Apples
What are the pollution sources in apple production, and what sustainable practices can
reduce pollution?
The main pollution concern for apple growers is pesticides.
Key apple pests in the Upper Midwest include plum curculio, codling moth, and apple
maggot. Leafrollers, aphids, leafminers, leafhoppers, scale insects, and spider mites can
also cause damage in apple orchards. And diseases such as fire blight, apple scab, and
powdery mildew can destroy the crop or make it unmarketable. (See
http://cecommerce.uwex.edu/pdfs/A2116.PDF, or
http://cecommerce.uwex.edu/pdfs/A2179.PDF.)
For decades, apple growers have used a wide array of pesticides to control these insects,
diseases, and weeds. But since the 1970s scientists, farmers, and consumers have all
become increasingly aware that pesticides can cause both environmental and human
health problems. As a result, some apple growers are seeking ways to grow apples using
fewer and less toxic pesticides.
The array of techniques and tools farmers use to get a good crop with minimal use of
pesticides is called Integrated Pest Management, or IPM.
IPM powerpoint
Activity 4: Economic threshold calculation
Activity 5: Apple IPM video and discussion
Fertilizer recommendations for tree fruits are low in comparison to most other
agricultural crops, so runoff and leaching from nutrient applications are not generally
considered to be problems of apple production in Wisconsin and Iowa. In addition, fruit
quality can deteriorate when too much nitrogen is applied. Thus, most mature
Midwestern orchards are not fertilized unless tissue testing indicates a nutrient
deficiency. See http://www.canr.msu.edu/vanburen/e-852.htm#part3,
http://cecommerce.uwex.edu/pdfs/A3565.PDF, or
http://www.spectrumanalytic.com/support/library/pdf/fertilizing_apple_trees.pdf for
information on nutrient recommendations for apple production. Including legumes such
as clover in the cover crop for the orchard floor can further reduce the need for nitrogen
fertilizer.
Soil erosion is a possible source of pollution from apple orchards. Apple trees yield
better when they do not compete with other vegetation within two or three feet of the tree
trunk. Most Wisconsin and Iowa orchards maintain 5 foot wide strips of bare ground in
the tree rows and 6 to 10 foot wide strips of grass groundcover between tree rows. If the
strips of groundcover are well maintained and planted along the contours, erosion can be
minimized. Some sustainable growers use mulch to suppress competing plant growth in
the tree row. Mulching reduces reliance on herbicides and the potential for soil erosion.
Although mulch can potentially provide cover for rodents and other pests, a 6 year study
of a cherry orchard in Michigan found that mulching increased yields over conventional
orchard floor management.
What are the interactions of living organisms in the system?
Typically, sustainable agro-ecosystems will try to work with species interactions and will
favor species and genetic diversity.
Everything in an ecosystem affects other parts of the ecosystem. Typically, production
agriculture has focused on the negative impacts of organisms other than the crop. In this
worldview, all non-crop plants are seen as weeds that compete for water, nutrients, and
sunlight, and all non-crop animals from insects to birds and mammals are seen as useless
at best and crop-destroying pests or disease carriers at worst.
There is some truth to this outlook. Weeds do compete with crop plants, and many types
of animals eat parts of the crop and can cause substantial yield losses. Agro-ecosystems
differ from natural ecosystems in that we require them to export a good portion of their
production for off-site human consumption. So farmers cannot afford to give weeds,
crop predators, and diseases a free hand.
On the other hand, it turns out that many non-crop organisms benefit crop production in
a variety of ways, such as by improving nutrient cycling and availability to the crop,
pollinating the crop, eating crop pests, providing habitat for beneficial species, and
reducing disease. Practices such as heavy use of synthetic fertilizers and pesticides and
mono-cropping may harm beneficial organisms as much as or more than pests.
The number of different species of plants, animals, and microorganisms in an ecosystem
is referred to as species diversity. There is also a different kind of variation, which is the
genetic diversity within a species or population (the individuals of one species in an
ecosystem).
Let’s take a look at both species diversity and genetic diversity in fresh market
vegetable production.
A popular model for sustainable vegetable production is the community supported
agriculture operation or CSA.
(http://www.extension.iastate.edu/Publications/PM1692.pdf).
CSAs promote diversity by:
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Planting a wide variety of crops. Because they try to supply most of the vegetable
needs for shareholders during the growing season, CSA farms grow a wide variety of
vegetables, herbs, flowers, and fruits. Over the course of one year, a typical CSA
farm will grow more than 30 different crops on less than 50 acres. The smallest
CSAs have less than 5 acres in production (Growing Harmony Farm
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http://www.newfarm.org/features/0404/carrots/index.shtml , Nevada, Iowa) and even
the largest CSAs in the Midwest (Angelic Organics
http://www.angelicorganics.com/index.html , Caledonia, Illinois and Harmony Valley
http://www.harmonyvalleyfarm.com/ , Viroqua, Wisconsin) have less than 100 acres
in crops.
Rotating crops. CSAs rotate crops to reduce disease and insect pressures.
Planting cover crops to reduce erosion, reduce weed pressure, and manage nutrient
cycling.
Avoiding use of broad-spectrum pesticides that can harm non-target species.
Deliberately encouraging beneficial organisms, from birds to insects, to help with
pest control.
Preserving and restoring natural habitats on the farm. Habitat preservation can
help make the farm more attractive to CSA members, and it also fits with the values
of most CSA farmers. Natural habitats usually contain far greater species diversity
than crop fields.
Planting numerous varieties of each crop, including open-pollinated and
heirloom varieties. CSAs usually value genetic diversity for several reasons. First
and most important, their customers value diversity and look for varieties that look
interesting and offer special flavors. Second, using several different varieties can
decrease the chance that a particular disease or pest will damage the whole crop.
Third, different varieties can often be harvested at different times. And finally, like
their customers, many growers take pleasure in the many different forms and flavors
one species can provide.
For example, in 2005 Harmony Valley CSA grew 16 varieties of tomatoes: 3
paste (a.k.a. Roma) tomatoes, 2 standard reds, 4 small cherry (a.k.a. grape), 2 gold,
and 4 heirlooms out in the field, and Sungold cherry tomatoes. August 20
newsletter, p. 2 http://www.harmonyvalleyfarm.com/NLTR/csa050827.pdf
Activity 6: Tasting Diversity
Seed Savers http://www.seedsavers.org/Aboutus.asp
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Comparison of plant communities
Pre-agricultural / “natural”
 Mix of perennial and annual species
 Variety of communities depending on soil type, climate and micro-climate, and site
history (prairies, savannahs, wetlands, forests, etc)
 Large number of species at one site, typically little or no exposed soil year-round
 Substantial genetic variation within most species
Conventional horticulture (vegetable production)
 Sequential mono-cultures (usually 2 or at most 3 species in rotation, sometimes only
one species)
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Mainly annual row crops, with bare soil between the rows and completely bare soil
exposed for 6 months of the year or more
 Little genetic variety within the species; often just one or two varieties grown of a crop
and high value placed on consistency of size and appearance
Sustainable horticulture in Wisconsin and Iowa
 Sequential mono-cultures (usually 3 to 6 species in rotation)
 Annual row crops rotated with perennials and small grains. Use of cover crops to
minimize amount of bare soil exposed in winter
 Interest in increasing genetic variety, including reintroduction of heirloom varieties as
well as breeding new varieties for diversity of flavor, appearance, and agronomic traits
such as disease resistance.
 Restoration of complex natural or partly natural plant communities around crop fields
What are the energy flows in the system?
Sustainable agro-ecosystems rely more on solar energy rather than on fossil fuels.
Sustainable systems minimize energy waste.
It is difficult to get recent detailed information about energy use in modern agriculture,
and most of the work that has been done on energy used in agricultural production looks
at field crops and livestock production rather than horticultural farms. Most modern fruit
and vegetable production relies on fossil fuels in a variety of ways, such as:
 Fuel and electricity to power equipment such as tractors
 Fertilizers and pesticides made from or with fossil fuels such as natural gas
 Fuel or electricity to heat greenhouses
 Plastic to cover hoophouses, act as mulch, and package produce
 Fuel to transport produce to market
 Electricity to keep produce cool
 Fuel and electricity to process produce
Certain farming and food system practices can provide substantial savings in fossil
energy use.
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Minimize use of nitrogen fertilizer and pesticides (see strategies recommended in the
nutrient cycling and pollution prevention segments)
 Recycle nutrients and resources on the farm
 Minimize transportation costs by selling to and buying from local sources
 Use renewable energy sources such as wind, solar, or biomass-fueled power
More than half of the energy in our food system is used not on the farm, but in
transportation, processing, storage and packaging, and home cooking.
Sustainable practices for the consumer
 Buy local foods, when possible
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Avoid excess packaging
Use energy-efficient appliances and techniques when possible
Use renewable energy sources, if possible (solar and wind power)