5.11 Animal Manures
5.12 90-120 Day Rule
5.13 Compost
5.14 Compost Tea
5.15 Vermicompost
5.16 Processed Animal Manures
5.17 Ratooning
5.18 Soil Conservation
5.19 Cover Cropping
5.20 Organic Mulches
5.21 Conservation Tillage
5.22 Contour Conservation and Strip Cropping
5.23 Mixed Cropping
5.24 Food Forests
5.25 Nutrient Management_Nitrogen and Trace Minerals
5.26 Genetic Engineering
5.2 Crop Rotation in Annual Crops
5.3 Crop Rotation in Perennial Crops
5.4 Biodiversity
5.5 Disease and Pest Management
5.6 Environmental Benefits and Considerations of Crop Rotations
5.7 Pesticide and Fertilizer Use Under Different Crop Rotations
5.8 Alley Cropping
5.9 Soil Building
5_Crop-Biodiversity
Crop Biodiversity
Overview
Title Image: Strips of oats and hay are interspersed with strips of corn to save soil and improve water quality and wildlife habitat on this field in northeast Iowa Credit: United States Department of Agriculture – Natural Resources Conservation Service; Public Domain
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Introduction
Lesson Objectives
Defend the need for genetic diversity in cropping systems.
Identify various cropping systems that promote genetic diversity.
Recognize the advantages and disadvantages related to genetic diversity.
Key Terms
conservation tillage - the minimal use of soil cultivation with crops
crop rotation - cycling through planting different types of crops for several years
mixed cropping - growing different types of plants in the same land
monoculture - a sequence where the same crop is planted for 3 consecutive years
polyculture - the process of growing multiple crops in a designated area to mimic the natural environment
ratooning - the process of cutting plant stems down to stimulate another round of growth
sequential cropping - growing various crops on the same land in different years, one after the other
vulnerability - plants’ susceptibility to pests and environmental conditions
Introduction
Expanding markets, new production technologies, and economic competition in recent decades have resulted in crop specialization, increased purchase of off-farm inputs, and production practices that often have adverse environmental consequences. Monoculture (successively growing the same crop on the same land), continuous row crops, and other intensive cropland uses have increased with the availability of commercial fertilizers to supply nutrient needs and chemicals to control pests. Crop rotations that include hay, grass sod, and other soil-conserving crops were abandoned by many producers as the demand for hay and forages declined. The choice between monoculture and rotating different crops on the same land depends on a broad range of economic and physical factors. And the choice of rotation frequently affects the use of fertilizer and pesticides.
Crop Rotation in Annual Crops
For producers of annual crops, complying with crop rotation standards is straightforward and often beneficial for crop health. Crop rotation refers to the sequencing of crops over time on a field or planting bed. Rotations typically mean that crops are not followed by a member of the same crop family. Sequential cropping is not unique to organic systems, as it is also practiced by many conventional farmers. However, organic systems are unique in that crop rotation is specifically required in the USDA organic regulations.
Crop rotation can
• interrupt insect life cycles.
• suppress soilborne plant diseases.
• prevent soil erosion.
• build organic matter.
• fix nitrogen.
• increase biodiversity of the farm.
Crop rotations are an important way to suppress insects and diseases. For example, farmers who raise potatoes will rotate the field out of solanaceous crops for at least 2 years before replanting potatoes. This helps reduce populations of insects, such as the Colorado potato beetle, and prevent diseases, such as late blight. Rotations with 3 to 5 years between the same crop may be needed to effectively reduce insect and disease levels.
Rotations also can be designed to increase soil fertility. A crop sequence that features soil-improving crops can counterbalance soil-depleting crops. Soil-improving crops include sod crops dominated by perennial grasses and perennial legumes. Sod crops in rotation build soil organic matter and reverse the decline that typically occurs when cultivated annual crops are grown year after year. Legumes, such as alfalfa, clovers, beans, and peas, are especially beneficial because they fix nitrogen from the atmosphere and make it available to subsequent crops. Even short-term, nonleguminous cover crops can provide benefits when used as part of the crop-rotation plan.
The best cover crops are specific varieties adapted to the soil, climate, and season. They are sown at a fairly high rate to cover the soil quickly and prevent erosion. When planning crop rotations, it is important to remember that cultivated row crops, such as vegetables, tend to degrade soil. Since the soil is open and cultivated between rows, microbes break down organic matter at a more rapid pace. Furthermore, row crops have modest root systems and consequently do not contribute enough new organic matter to replace that lost from the open soil between rows. In most cases, above-ground crop residues make only minor contributions to replacing lost organic matter.
In contrast, cereals and cover crops are more closely spaced and have more extensive root systems than row crops, greatly reducing the amount of soil exposed to degradation. In addition, these crops receive little or no cultivation after planting, which reduces organic-matter loss even more. As a result, cereals and green manures can be considered neutral crops, replacing soil organic matter at roughly the same rate at which it breaks down. Crops that make a perennial sod cover, such as grasses, clovers, and alfalfa, not only keep the soil entirely covered but also have massive root systems that produce far more organic matter than is lost.
Incorporating sod crops as a fundamental part of a crop rotation not only builds soil but also supports weed-control strategies. Weed control improves because the types of weeds encouraged by row-cropping systems are usually adapted to growing in a sod/hay crop. To make the most efficient use of sod crops, it is necessary to include livestock in the system or to find a market for the hay. Livestock will assist in transferring (via manure) nutrients from one part of the farm to another. The major drawback to selling hay is that the nutrients it contains are shipped off the farm.
Crop Rotation in Perennial Crops
For producers of organic perennial crops, the requirement for crop rotation can be confusing. Farmers should implement practices that will maintain soil organic matter, control pests, conserve nutrients, and protect the soil against erosion. For growers of annual crops, those practices typically include crop rotation, but other practices can be substituted if rotation is not practical.
Some perennials will be part of a long-term crop rotation, which may last a few years or even decades. Asparagus, for example, is a perennial that can be productive for 15 years or more. When a field is taken out of asparagus production, it is typically planted with another crop to reduce the incidence of soilborne disease. That practice is considered a long crop rotation. Several other perennials, such as strawberries, Echinacea, and lavender, are not required to have a cover crop because they are typically part of a long crop rotation.
Other types of perennials—those that will not be part of a crop rotation—may require additional practices to ensure soil conservation and biodiversity in the cropping system. This is important with large perennials, such as trees, that have large drive rows between the crop rows. For example, organic farmers must have a cover crop (often grass) between the rows of trees in an orchard. Crops that are required to have a cover crop between crop rows include caneberries, grapevines, blueberries, tree fruits, and nut trees.
Some perennial crops, such as alfalfa, develop a canopy that covers the ground and prevents soil erosion. Such crops are not required to be rotated with other crops.
Biodiversity
Many organic farmers actively manage their farms to increase biodiversity, due to its many benefits. Biodiversity plays a particularly crucial role in pest management. Although farmers are encouraged to have diverse systems, there are no specific requirements, standards, or monitoring practices. Diverse agricultural systems support strong populations of predators and parasites that help keep pest populations at manageable levels. This approach is proactive rather than reactive because a diverse system reaches an equilibrium that prevents pest outbreaks from becoming too severe. Birds and bats can keep insect populations low. Raptors can scare away fruit-eating birds. Coyotes, owls, and foxes can keep rodent populations under control. These animals can be encouraged to improve the plants' vulnerability because plants are providing needed shelter, water, and habitat.
Organic producers increase biological diversity in the plant canopy by planting a diversity of crops and plant varieties in any given season. Use of cover crops and hedgerows also adds biodiversity. The diversity of vegetation, combined with reduced use of broad-spectrum pesticides, increases the diversity of insects and spiders in the plant canopy. Introducing beneficial insects and providing habitat for them to become established will increase biodiversity. To promote biodiversity in the soil, it is helpful to minimize tillage, introduce microorganisms in compost, and avoid broad-spectrum pesticides. These practices will increase the variety of bacteria, fungi, and invertebrates in the soil.
Disease and Pest Management
In many field crop and vegetable systems, maintaining a diverse, healthy ecosystem and using well-timed cultural practices are sufficient for pest management. Pests may not be eliminated, but damage levels are low enough to be tolerated. Organic producers maintain that organic soil-building practices will result in crops that are properly nourished and thereby less susceptible to attack by pests and diseases. Natural biological pest control arises in a healthy organic system in the form of an active complex of natural predators and parasites that suppress pest populations. Incorporating habitat and food sources for beneficial insects into the farm, known as farmscaping, can provide long-term benefits.
Environmental Benefits and Considerations of Crop Rotations
Crops face danger of extensive damage or destruction from a variety of sources including weeds, pests, diseases, adverse environmental conditions, and unfavorable weather. Potential crop yields can be seriously restricted by a lack of crop protection.. Planned crop rotations can increase yields, improve soil structure, reduce soil loss, conserve soil moisture, reduce fertilizer and pesticide needs, and provide other environmental and economic benefits. However, crop rotations may reduce profits when the acreage and frequency of highly profitable crops are replaced with crops earning lower returns. Many crop rotations reduce soil loss and are an option for meeting conservation compliance on highly erodible land. The growth of hay, small grain crops, or grass sod in rotation with conventionally tilled row crops reduces the soil’s exposure to wind and water and decreases total soil loss. While beneficial, crop sequencing can be complex and require more knowledge about plants and growing (Figure 5.5.2).
These rotations, however, are a desirable option to farmers only when profitable markets exist or the conservation crops can be utilized by on farm livestock enterprises. Alternating wheat and fallow is a common practice for conserving soil moisture in regions with low rainfall. Applying tillage practices to minimize evaporation or transpiration from idle land in one season increases the amount of stored soil moisture
available for the crop in the following season.
The ability of legume crops to fix atmospheric nitrogen and supply soil nitrogen needs for subsequent crops is well documented. The plowdown of established alfalfa or other legumes can provide carryover nitrogen for a crop that requires high levels of nitrogen, such as corn. Research has shown that soybeans can be managed to fix 90 percent of their nitrogen needs and provide a soil nitrogen credit of 20 pounds or more per acre for a subsequent crop (Heichel, 1987). However, soybeans grown in rotation with corn where soils are already rich in nitrogen have not been shown to fix significant amounts of nitrogen.
Crop rotations affect pest populations and can reduce the need for pesticides. Different crops often break pest cycles and prevent pest and disease organisms from building to damaging levels. Treatment for corn rootworm, the most common insecticide treatment on corn, normally only requires alternating another crop to sufficiently reduce root-worm survival rates to levels that do not require insecticide treatment. Hay and grass sod grown in rotation with corn, however, may increase the need for other corn insecticides to treat other pests.
Besides providing erosion control, small grains, hay, and grass sod are competitive with broadleaf weeds and may help control weed populations in subsequent crops. These crops are usually harvested or can be cut before weeds reach maturity and produce seed for germination the following season. Weeds on prior idle acres or fallow land may be controlled by either cutting or tilling to reduce weed infestations the following year. Sometimes, herbicides are used to kill existing vegetation on idle land (chemical fallow)
in lieu of mechanical methods.
Rotations also can reduce financial risk and provide a more sustainable production system. Since adverse weather or low market prices are less likely to affect all crops simultaneously, the diversity of products resulting from crop rotation can reduce risk.
Pesticide and Fertilizer Use Under Different Crop Rotations
Crop rotation is often key to a sustainable agricultural production system and can reduce the need for fertilizer and pesticides. Fertilizer applications are often adjusted for prior nitrogen-fixing crops. Fewer pesticides may be needed when rotations break pest cycles or reduce infestation levels.
Alley Cropping
Alley cropping is defined as the planting of rows of trees and/or shrubs to create alleys within which agricultural or horticultural crops are produced. Alley cropping systems are sometimes called intercropping, especially in tropical areas. The trees produced through alley cropping may include valuable hardwood veneer or lumber species; fruit, nut or other specialty crop trees/shrubs; or desirable softwood species for wood fiber production. As trees and shrubs grow, they influence the light, water, and nutrient regimes in the field. These interactions are what sets alley cropping apart from more common monocropping systems.
Alley cropping can vary from simple systems, such as an annual grain rotation between timber tree species, to complex multilayered systems that can produce a diverse range of agricultural products. It is especially attractive to producers interested in growing multiple crops on the same acreage to improve whole-farm yield. Growing a variety of crops in close proximity to each other can create significant benefits to producers, such as improved crop production and microclimate benefits and help them manage risk.
Soil Building
For centuries before the advent of chemical fertilizers, farmers supplied all the nutrients for their crops solely by adding organic matter to the soil. As fresh organic matter, such as crop residues, decomposes, it forms a stable substance called humus. Organic matter can be added to soils with compost, animal manures, or green manures. Adding organic matter is a fundamental way to build soils. Organic matter provides food for microorganisms, such as fungi and bacteria, and macroorganisms, such as earthworms. As these diverse soil organisms decompose organic matter, they convert nutrients into forms that are available to plants. Soils high in organic matter also have improved water-holding capacity, helping plants resist drought.
Green Manures
Green manures are crops grown specifically for soil improvement. They are typically incorporated into the soil after they have produced a large amount of biomass or fixed a significant amount of nitrogen in the case of legumes. Managing green manure crops to increase organic matter and provide the maximum amount of nitrogen to the following crop is both an art and a science.
Annual grasses, small grains, legumes, and other useful plants like buckwheat can be inserted into the cropping sequence to serve as green manures. Their roots pull nutrients from deeper soil layers, and the tops are plowed into the soil to add organic matter and a stable source of nutrients. In particular, deep tap-rooted crops such as alfalfa, sweet clover, rape, and mustard are known to extract and use minerals from the deeper layers of soil.
Legumes add nitrogen to the soil. Nitrogen accumulations by leguminous cover crops can range from 40 to 200 pounds of nitrogen per acre. The amount of nitrogen captured by legumes depends on the species of legume grown, the total biomass produced, and the percentage of nitrogen in the plant tissue. Cultural and environmental conditions that limit legume growth—such as a delayed planting date, poor stand establishment, and drought—will reduce the amount of nitrogen produced. Conditions that favor high nitrogen information production include a good stand, optimum soil nutrient levels and soil pH, good nodulation, and adequate soil moisture.
Animal Manures
Conservation of manure and its proper application are key means of recycling nutrients and building soil. Farms without livestock often buy manure or compost because they are considered to be among the best fertilizers available, though sole reliance on fertilizers from other farms can have its drawbacks like cost, availability, and transportation.
Manures from conventional systems are allowed in organic production, including manure from livestock grown in confinement and from those that have been fed genetically engineered feeds. Manure sources containing excessive levels of pesticides, heavy metals, or other contaminants may be prohibited from use. Such contamination is likely present in manure obtained from industrial-scale feedlots and other confinement facilities. Certifiers may require testing for these contaminants if there is reason to suspect a problem.
Herbicide residues have been found in manures and manure-based composts. One type—aminopyralid—is used in pastures for control of broadleaf weeds. Grass and corn are not affected by the herbicide, and cows are not affected when they eat the grass or silage. However, the herbicide can be present in their manure in concentrations high enough to stunt the growth of tomatoes, peppers, and other susceptible broadleaf crops.
If a manure source is suspected of being contaminated with excessive amounts of prohibited substances, appropriate testing should be conducted. If test results indicate that the manure is free of excessive contamination, and it is subsequently used in production, the test results should be kept on file.
Used properly, manures can replace all or most needs for purchased fertilizer, especially when combined with a whole-system fertility plan that includes crop rotation and cover cropping with nitrogen-fixing legumes. Manure is typically applied just ahead of a crop requiring high fertility, such as corn or squash. Manures also can be applied just prior to a cover crop planting. Incorporating the manure as soon as possible after application, rather than allowing it to remain on the soil surface, will conserve the maximum amount of the nitrogen.
Although manure is an excellent fertilizer for crops, and it has been used that way for centuries, manure may harbor microorganisms that are pathogenic to humans. To minimize the possibility of illness due to organic foods, there are strict regulations on the use of manure in organic crops.
90-120 Day Rule
Application of manure to organic crops is restricted by what is known as the 90–120-day rule, as described in § 205.203(c)(1):
“You may not apply raw, uncomposted livestock manure to food crops unless it is:
1. Incorporated into the soil a minimum of 120 days prior to harvest when the edible portion of the crop has soil contact; OR
2. Incorporated into the soil a minimum of 90 days prior to harvest of all other food crops.”
Incorporation is generally assumed to mean mechanical tillage to mix the manure into the soil. This is important for crops that have soil contact which include leafy greens, melons, squash, peas, and many other vegetables. Any harvestable portion of a crop that can be splashed with soil during precipitation or irrigation might be considered to have soil contact. Crops that do not have soil contact include tree fruits and sweet corn.
The 90- and 120-day restrictions apply only to food crops; they do not apply to fiber crops, cover crops, or to crops used as livestock feed.
Compost
Perhaps no other process is more closely associated with organic agriculture than composting. Composting is one of the most reliable and time-honored means of conserving nutrients to build soil fertility. Because matured, well-made compost is a stable fertilizer that will not burn plants and because composting kills most human and plant pathogens, compost can safely be used as a side-dress fertilizer on food crops.
Animal manures used in organic crop production often are composted before use, in part because some types of raw manure will burn plants if applied directly to crops. Composting reduces the number of viable weed seeds, creates a uniform product with predictable nutrient levels, and eliminates worries about human pathogens. If manures are composted according to USDA organic regulations, then they are considered compost, not manure, and may be applied without restrictions. If manure is aged but not composted according to the regulations, then the material is still considered manure and must be applied in accordance with the 90–120-day rule explained above.
The composting procedures are adapted from U.S. Environmental Protection Agency (EPA) and USDA’s Natural Resources Conservation Service (NRCS) guidelines for composting biosolids. This policy was established to ensure the elimination of pathogens that cause illness in humans. The regulations define compost as “the product of a managed process through which microorganisms break down plant and animal materials into more available forms suitable for application to the soil...” Compost used in organic production must be made according to the criteria set out in § 205.203(c)(2). This section of the regulations specifies that:
- “The initial carbon: nitrogen ratio of the blended feedstocks must be between 25:1 and 40:1.
- The temperature must remain between 131 °F and 170 °F for 3 days when an in-vessel or a static-aerated-pile system is used.
- The temperature must remain between 131 and 170°F for 15 days when a windrow composting system is used, during which period the windrow must be turned at least five times.”
Organic farmers often maintain a compost pile on the farm as an efficient and cost-effective way to retain nutrients on the farm and build soil. If compost feedstocks include raw manure, they must be composted in the method detailed above. This composting process must be explained in a system plan and documented with temperature records. If those requirements are not met, then the resulting compost must be applied according to the 90-120-day raw manure rule. If compost feedstocks do not include raw animal manures, then the resulting compost is considered plant material and there are no restrictions on its use.
Compost Tea
Some organic farmers apply compost teas to crops or soil to increase the populations of beneficial microbes. If compost tea will be applied to organic crops, it is critical that the compost used to produce the extract has been made according to USDA organic regulations. The procedures for making both the compost and the compost tea must be explained in your OSP. Applications of teas made from uncomposted manure must follow the 90-120-day rule. The tea extract may need to be tested to ensure that it is free of dangerous pathogens, particularly if the tea has been made with compost tea additives. The additives, such as molasses, provide nutrients for microbes and thereby increase their rate of growth. There is some concern that any human pathogens present will grow more abundantly in a tea made with these additives. Further details on the recommendations for the use of compost tea are available in the NOP publications listed at the end of this chapter.
Vermicompost
Vermicompost is compost that uses worms to digest the feedstocks. Since feedstocks may include animal manures, there has been debate as to whether the 90-120-day rule should apply to vermicompost. The NOP has issued the following guidance: feedstocks for vermicompost materials may include organic matter of plant or animal origin.
Feedstocks should be thoroughly macerated and mixed before processing. Vermicomposting systems depend upon regular additions of thin layers of organic matter at 1- to 3-day intervals. Doing so will maintain an aerobic environment and avoid temperature increases above 35 °C (95 °F), which will kill the earthworms. The composting process must be described in the OSP, reviewed by the certifier, and well documented on the farm. Further details are available in the NOP publications listed at the end of this chapter.
Processed Animal Manures
Heat-treated, processed manure products may be used in organic production. There is no required interval between application of processed manure and crop harvest. From the standpoint of the farmer, of course, these inputs would be applied well before harvest, so that the nutrients would be available to the crop. To be considered processed, the manure must be heated to 150 °F for 1 hour and dried to 12 percent moisture or less.
Ratooning
Ratooning is a production practice that is sometimes used on plants like sugarcane and okra. The process involves cutting stems down in mid-summer. Plants are then fertilized after being ratooned to support plant growth. This process rejuvenates the plant to stimulate another round of harvest on new growth in the later summer to early fall and is common in commercial growing.
Soil Conservation
Careful conservation and management of crop residues is part of organic soil management, since this residue plays a valuable role in improving and protecting the soil. The key to soil conservation is to keep the ground covered for as much of the year as possible. Organic farmers have long recognized the value of basic soil conservation. There are many practices that help conserve soil, including cover crops, mulches, conservation tillage, contour plowing, and strip cropping.
Since water erosion is initiated by raindrop impact on bare soil, any management practice that protects the soil from raindrop impact will decrease erosion and increase water entry into the soil. Mulches, cover crops, and crop residues all serve this purpose well. A major limitation of organic row-crop farming is that cultivation is used for weed control, since herbicides are not allowed. This cultivation creates and maintains bare ground, which increases the likelihood of soil erosion. By contrast, soil that is covered with an organic mulch of crop residue, such as that typically found in no-till fields, is less likely to erode. Organic no-till systems have yet to be perfected for annual row crops, but they work well for perennial fruit crops and pasture, allowing for year-round ground cover and virtually no soil erosion.
Cover Cropping
Cover crops are single species or mixtures of plants grown to provide a vegetative cover between perennial trees, vines, or bushes; between annual crop rows; or on fields between cropping seasons. The vegetative cover on the land prevents soil erosion by wind and water, builds soil fertility, suppresses weeds, and provides habitat for beneficial organisms. Cover crops also can help reduce insect pests and diseases, and legume cover crops fix nitrogen.
Any crop grown to provide soil cover is considered a cover crop, regardless of whether that crop is later incorporated into the soil as a green manure. Both green manures and other types of cover crops can consist of annual, biennial, or perennial herbaceous plants grown in a pure or mixed stand during all or part of the year. When cover crops are planted to reduce nutrient leaching following a cash crop, they are termed “catch crops.” This type of cover crop is typically grown over the winter when the field would otherwise be unoccupied.
Organic Mulches
Organic mulches cover the soil and provide many of the same benefits as cover crops, especially the prevention of soil erosion. Many organic materials—such as straw, leaves, pine needles, and wood chips—can be effective mulches. Straw and other materials that are easily decomposed are applied to strawberries and vegetables during the growing season.
The mulch can be tilled in at the end of the season, where it will quickly decompose. Wood chips, because they decompose very slowly, are more commonly applied to perennial crops such as blueberries, where they will not be tilled in. Applying organic mulch can be labor-intensive. Tree fruit growers sometimes mow the drive rows and blow the green clippings into the tree rows, which automates the mulching process.
Heavy mulches can be a benefit by suppressing weed growth, or a nuisance by providing a haven for slugs. Organic mulches keep the soil cool, which may be a boon for blueberries in hot climates and a drawback for tomatoes in cool spring weather. Organic mulches have a beneficial long-term effect because they add nutrients to the soil as they decompose.
Mulches of high-carbon material may have the opposite effect because they tie up nitrogen during the decomposition process. However, this should not be a problem if mulches are used properly—that is, placed on top of the soil, and not incorporated.
Conservation Tillage
In conservation tillage, crops are grown with minimal soil cultivation. This is also known as no-till, minimum till, incomplete tillage, or reduced tillage. When the amount of tillage is reduced, the residues from the plant canopy are not completely incorporated into the soil after harvest. Crop residues remain on top of the soil and prevent soil erosion, a practice known as crop residue cover. The new crop is planted into this stubble or small strips of tilled soil within the stubble.
Contour Conservation and Strip Cropping
Slope plays a role in soil conservation, in that flat ground erodes less than sloping ground with equal amounts of ground cover. Contour plowing is the practice of plowing across a slope following its elevation contour lines, rather than straight up and down the slope. The cross-slope rows formed by contour plowing slow water runoff during rainstorms to prevent soil erosion.
Strip farming, also known as strip cropping, alternates strips of closely sown crops, such as hay or small grains, with strips of row crops, such as corn, soybeans, or cotton. Strip farming helps prevent soil erosion by creating natural dams for water, helping to preserve the soil.
Mixed Cropping
The growing of several crops simultaneously in the same field but not in rows is called mixed cropping. Mixed cropping, including intercropping, is the oldest form of systemized agricultural production and involves the growing of two or more species or cultivars of the same species simultaneously in the same field. However, mixed cropping has been little by little replaced by sole crop systems, especially in developed countries. Some of the advantages of mixed cropping are, for example, resource use efficiency and yield stability, but there are also several challenges, such as weed management and competition.
Food Forests
Modern agriculture has leaned heavily on monoculture field cropping. Many have found polyculture to be a natural solution for modern issues like soil water conservation, nutrient deficiencies in soil, and disease and pest management. Trees can provide many benefits in gardens and in urban environments. They produce fruit, like apples, peaches and figs, and also provide shade and wildlife habitat.
Food forests support forest ecosystems and connect communities with nature. Trees of different sizes produce nuts and fruit, while their shade can support a variety of fresh, flavorful mushrooms, herbs, and berries. Trees improve air quality and help soil retain water.
Nutrient Management: Nitrogen and Trace Minerals
Although organic matter plays an important role in building productive soils, there are specific crops and soil types that will benefit from additional applications of specific nutrients. Organic farmers are allowed to use a variety of fertilizers to provide micronutrients to their crops. Before applying micronutrients, soil deficiencies must be documented through soil tests, plant tissue tests, observing the condition of plants, or evaluating crop quality at harvest.
Nitrogen is often a limiting nutrient, especially for vegetables and other row crops. Including legumes in the rotation can help to ensure sufficient nitrogen for the following crop. Biological nitrogen fixation in legumes results from a symbiotic relationship between the plant and Rhizobium bacteria. These bacteria “infect” the roots of legumes, forming nodules. The bacteria then fix nitrogen from the air, which results in sufficient nitrogen both for their own needs and for subsequent crops.
The inoculation of legume seed may be necessary to optimize nitrogen fixation. It is important to purchase an inoculant appropriate to the kind of legume being planted to ensure it is not genetically modified. Genetically modified inoculants are prohibited in organic production.
Genetic Engineering
The planting of GM crops is regulated—new varieties may not be widely planted until they’ve been approved by USDA. If conventional seed is planted, the certifier will request proof that it is not genetically engineered. This verification is becoming more important each year, as the number of genetically modified (GM) crops increases. The use of GM seeds is prohibited in organic agriculture, and it is the responsibility of organic growers to make certain that the crops they grow are not genetically engineered. GM crops that are now being planted or will soon be available include alfalfa, beets, corn, soybeans, papaya, plum, rapeseed, tobacco, potato, tomato, squash, cotton, and rice. This list is expected to change, as genetically engineered versions of several other crops have been developed but have not yet been released for commercial production. The most current information about GM crops is maintained by the USDA Animal and Plant Health Inspection Service (APHIS).
Seed companies that develop a new variety of genetically modified seeds must submit a petition to APHIS before that seed can be distributed to the public. Genetic engineering is considered an excluded method and is defined as a variety of methods used to genetically modify organisms or influence their growth and development by means that are not possible under natural conditions or processes and are not considered compatible with organic production. Such methods include cell fusion, microencapsulation and macroencapsulation, and recombinant DNA technology (including gene deletion, gene doubling, introducing a foreign gene, and changing the positions of genes when achieved by recombinant DNA technology). Such methods do not include the use of traditional breeding, conjugation, fermentation, hybridization, in vitro fertilization, or tissue culture.
With certified organic production, if it is necessary to use conventional seeds, it is essential to verify that the variety has not been genetically engineered and to keep documentation of this verification, as your inspector will ask to see it. Seed companies that have taken the Safe Seed Pledge may be convenient sources of non-GMO seeds. The Safe Seed Pledge was developed by the Council for Responsible Genetics and has been signed by numerous seed companies.
Dig Deeper
Attributions
Title Image: Strips of oats and hay are interspersed with strips of corn to save soil and improve water quality and wildlife habitat on this field in northeast Iowa, Credit: United States Department of Agriculture – Natural Resources Conservation Service; Public Domain
4.2 Crop Rotations by the United States Department of Agriculture is in the Public Domain.
Alley Cropping by the United States Department of Agriculture is in the Public Domain.
Guide for Organic Crop Producers by the United States Department of Agriculture is in the Public Domain.
"Sustainable Mixed Cropping Systems for the Boreal-Nemoral Region" by Lizarazo, et. al. is licensed CC BY 4.0.
Trees and Food Forests by the United States Department of Agriculture is in the Public Domain.