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Research and Science A UERNATIVE AGRICULTURE iS a systems approach to farming that is more responsive to natural cycles and biological interactions than conven- tional farming methods. For example, in alternative farming systems, farm- ers try to integrate the beneficial aspects of biological interaction among crops, pests, and their predators into profitable agricultural systems. Alter- native farming is based on a number of accepted scientific principles and a wealth of empirical evidence. Some of both are presented in this chapter. The specific mechanisms of many of these phenomena and interactions need further study, however. In general, much is known about some of the components of alternative systems, but not nearly enough is known about how these systems work as a whole. Examples of practices or components of alternative systems that the com- mittee has considered are listed below. Some of these practices are already part of conventional farming enterprises. These practices include: Crop rotations that mitigate weed, disease, and insect problems; in- crease available soil nitrogen and reduce the need for synthetic fertiliz- ers; and, in conjunction with conservation tillage practices, reduce soil erosion. Integrated pest management (IPM), which reduces the need for pesti- cides by crop rotations, scouting, weather monitoring, use of resistant cultivars, timing of planting, and biological pest controls. Management systems to improve plant health and crops' abilities to resist pests and disease. Soil-conserving tillage. Animal production systems that emphasize preventative disease man- agement and reduce reliance on high-density confinement, costs asso- ciated with disease, and need for use of subtherapeutic levels of antibi- otics. 135

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136 ALTERNATIVE AGRICULTURE ADVOCATES AND PRACTITIONERS OF ALTERNATIVE FARMING SYSTEMS Individuals who adhere to philosophies that advocate nonconventional farming practices. Some farmers never changed to the chemically intensive, specialized approach to crop and animal production that currently domi- nates U.S. agriculture. These farmers include followers of traditional organic farming movements, such as biodynamic agriculture and the systems ad- vocated by Albert Howard and Eve Balfour [Balfour, 1976; Howard, 1943~. These individuals also include farmers who farm organically because of religious beliefs, such as some Amish and Mennonite farmers of Pennsyl- vania and the Midwest. Others have practiced a generic form of organic farming not associated with any of the established organic movements tHarwood, 1983~. Farmers looking for new ways to reduce production costs. Throughout the United States, individual farmers have recognized that heavy purchases of off-farm inputs can put them in a less competitive economic position. These farmers have modified their farming practices, often in innovative ways, to reduce production costs. Examples include a wide variety of conservation tillage systems; the use of legume-fixed nitrogen through ro- tations; interplanting; the substitution of manures, sewage sludges, or other organic waste materials for purchased inorganic fertilizers; and the use of IPM systems and biological pest control. Farmers responding to consumer interest in chemical-free organic pro- duce. Many enterprising farmers producing agronomic and horticultural crops, milk, eggs, poultry, beef, and pork without synthetic chemical inputs have taken advantage of the fact that many consumers and businesses are willing to pay higher prices for these sorts of products. In response to market demand, several commercial supermarket chains have recently be- gun to market produce grown with no or very low levels of certain syn- thetic chemical pesticides at prices roughly comparable to those of conven- tionally grown produce. Farmers responding to concerns about the adverse impact of many con- ventional farming practices on the environment. Environmental groups and soil conservation organizations have raised public awareness of the envi- ronmental hazards of conventional agricultural practices. As a result of these hazards and personal concern for the environment, some farmers have adopted alternative farming practices that are helping to reduce the deteri- oration of our nation's soil and water resources. University research scientists. Critics have attacked the colleges and schools of agriculture in the land-grant universities and the U.S. Department of Agriculture (USDA} for not researching farming systems that protect the environment and reduce dependence on synthetic chemical inputs. But many individuals at these institutions have been investigating for years practices and systems that have alternative agricultural applications. Exam-

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RESEARCH AND SCIENCE pies include integrated pest management [IPM], biological controls of pests, rotations, nitrogen fixation, timing of fertilizer applications, disease- and stress-resistant plant cultivars, conservation tillage, and use of green manure crops. These research efforts have fostered some important changes in U.S. agriculture. As greater effort is made toward implementing the results of this research, more progress can be expected in the future. Much of the scientific knowledge of alternative practices summarized below is the result of research at the land-grant universities and the USDA. Alternative agriculture organizations. Groups such as Practical Farmers of Iowa, the Land Stewardship Project, the Institute for Alternative Agriculture, the Regenerative Agriculture Association, the Center for Rural Affairs, the Land Institute, and many others have worked to provide farmers with information on alternatives. They have organized research and demonstra- tion projects, lobbied state legislatures and Congress for research and dem- onstration support, and produced numerous technical publications and reports with information designed to help and encourage farmers to adopt alternatives. 137 Genetic improvement of crops to resist pests and diseases and to use nutrients more effectively. Many alternative agricultural systems developed by farmers are highly productive (see the boxed article, "Advocates and Practitioners of Alterna- tive Farming Systems," and Part Two). They typically share much in com- mon, such as greater diversity of crops grown, use of legume rotations, integration of livestock and crop operations, and reduced synthetic chemi- cal use. Although many practices show great promise, the scientific bases for many of them are often incompletely understood. During the last four decades, agricultural research at the land-grant uni- versities and the USDA has been extensive and very productive. Most of the new knowledge has been generated through an intradisciplinary ap- proach to research. Scientists in individual disciplines have focused their expertise on one aspect of a particular disease, pest, or other agronomic facet of a particular crop. Solving on-farm problems, however, requires more than an intradisciplinary approach. Broadly trained individuals or interdis- ciplinary teams must implement the knowledge gained from those in indi- vidual disciplines with the objective of providing solutions to problems at the whole-farm level. This interdisciplinary problem-solving team approach is essential to understanding alternative farming practices. Agricultural research has not been organized to address this need except in a few areas, such as IPM, the use of organic residues as an alternative nutrient source, and the use of leguminous green manure crops and rota- tions for erosion control and as a nitrogen source. Even this research has not significantly contributed to the adoption of alternative agricultural sys- tems for two principal reasons. First, most research has focused on individ-

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138 ALTERNATIVE AGRICULTURE ual farming practices in isolation and not on the development of agricultural systems. This is because of the high expense of farming systems research, the intradisciplinary nature of university research, and lack of resources. Second, most research results have been implemented under policies that encouraged ever-increasing per acre yields as the best way to increase farm profits and the world food supply. In contrast, alternative farming research must include the interaction and integration of all farm operations and must consider the more comprehen- sive goals of resource management, productivity, environmental quality, and profitability with minimal government support. Only a limited amount of research has taken this comprehensive approach. Nevertheless, the sci- entific literature about specific farm practices and the empirical evidence from individual operators illustrate the efficacy and potential of alternative farming methods and provide the foundation on which to build a program of alternative farming research. Important elements of the scientific knowledge base relevant to further development of alternative agricultural systems are briefly reviewed in the following sections. Knowledge of biological systems and the management of their interactions throughout agricultural ecosystems are emphasized. CROP ROTATION Crop rotation is the successive planting of different crops in the same field. A typical example would be corn followed by soybeans, followed by oats, followed by alfalfa. Rotations are the opposite of continuous cropping, which involves successively planting the same field with the same crop. Rotations may range between 2 and 5 years (sometimes more) in length and generally involve a farmer planting a part of his or her land to each crop in the rotation. Rotations provide many well-documented economic and envi- ronmental benefits to agricultural producers (Baker and Cook, 1982; Heady, 1948; Heady and Jensen, 1951; Heichel, 1987; Kilkenny, 1984; Power, 1987; Shrader and Voss, 1980; Voss and Shrader, 1984~. Some of these benefits are inherent to all rotations; others depend on the crops planted and length of the rotation; and others depend on the types of tillage, cultivation, fertilization, and pest control practices used in the rotation. When rotations involve hay crops, on-farm livestock or a local hay market are generally required to make the hay crop profitable. Much of the literature on crop rotations refers to the rotational effect (Heichel, 1987; Power, 1987~. This term is used to describe the fact that in most cases rotations will increase yields of a grain crop beyond yields achieved with continuous cropping under similar conditions. This rota- tional effect has been shown to exist whether rotations include nonlegumi- nous or leguminous crops. Corn following wheat, which is not a legume, produces greater yields than continuous corn when the same amount of fertilizer is applied (Power, 1987~. The increase in crop yields following a leguminous crop is usually greater than expected from the estimated quan-

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RESEARCH AND SCIENCE 139 Between 40 and 45 percent of the ld.S. corn crop is grown in continuous monoculture. Corn grown continuously generally requires greater use of fertilizers and pesticides than corn grown in rotation. This corn field is 10 miles from Kearney, Nebraska, which can be seen on the horizon. Credit: U.S. Department of Agriculture. tity of nitrogen supplied (Cook, 1984; Goldstein and Young, 1987; Heichel, 1987; Pimente] et al., 1984; Voss and Shrader, 1984~. In fact, yields of grains following legumes are often 10 to 20 percent greater than continuous grain regardless of the amount of fertilizer applied. Many factors are thought to contribute to the rotational effect, including increased soil moisture, pest control, and the availability of nutrients. It is generally agreed, however, that the most important component of this effect is the insect and disease control benefits of rotations (Cook, 1984, 1986~. The increase in soil organic matter, particularly in socI-based rotations, may

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140 ALTERNATIVE AGRICULTURE Contour strip cropping can reduce erosion and pest infestation. When a legume is included in a rotation, such as the corn- wheat-alfalfa rotation shown here, nitrogen fertilizer needs can be decreased. Credit: Grant Heilman. be the basis for the improved physical characteristics of soil observed in rotations. This may account for some yield increase. Certain deep-rooted leguminous and nonTeguminous crops in rotations may use soil nutrients from deep in the soil profile. In the process, these plants may bring the nutrients to the surface, making them available to a subsequent shallow- rooted crop if crop residue is not removed. Another benefit common to ah rotations is the control of weeds, insects, and diseases, particularly insects and diseases that attack the plant roots (Cook, 1986~. This pest control is achieved primarily through the seasonal change in food source (the crop), which usually prevents the establishment of destructive levels of pests. As root disease and insect damage are re- duced, the healthy root system is better able to absorb nutrients in the soil, which can reduce the rates of fertilizers needed (Cook, 1984~. Healthy root systems also take up nutrients more effectively, thus reducing the likelihood of nutrient leaching out of the root zone. Rotations with particular crops or crop combinations can provide addi- tional benefits. Legumes in rotations will fix nitrogen from the atmosphere into the soil. The amount of nitrogen fixed depends on the legume and the

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RESEARCH AND SCIENCE 141 management system; however, without any additional nitrogen fertilizers, leguminous nitrogen can support high grain yields (Heichel, 1987; Voss and Shrader, 1984~. The length of the rotation and yield expectations of the farmers, however, influence the level and acceptability of these yields. Hay and forage crops and closely sown field grain crops, such as wheat, barley, and oats, can provide some soil erosion control benefits in rotations. In some eroding areas with steep terrains, the practice of strip cropping corn (a row crop) with wheat (a closely sown crop) or a hay crop, such as alfalfa, is a common use of rotations to slow erosion. It must be stressed, however, that tilIage practices greatly influence the erosion control benefits of crops planted in rotations (Elliott et al., 1987~. For example, a rotation of corn, soybeans, and wheat is excellent for disease control but not for erosion control unless no tilIage or reduced tilIage is used. An indirect but important benefit of all rotations is that they involve diversification. The benefits of diversification are described in more detail later in this chapter. In general, however, diversification provides an eco- nomic buffer against price fluctuations for crops and production inputs as well as the vagaries of pest infestations and the weather. Rotations may have their disadvantages, however, particularly in the con- text of current government subsidies and requirements for federal program participation (see Chapters 1 and 4~. Rotations that involve diversifying from cash grains to crops such as leguminous hays with less market value involve economic tradeoffs (see Chapter 4~. Adopting the use of rotations may also require purchasing new equipment. As with all sound manage- ment practices, rotations must be tailored to local soil, water, economic, and agronomic conditions. PLANT NUTRIENTS Soil, water, and air supply the chemical elements needed for plant growth. Photosynthesis captures energy from the sun and converts it into stored chemical energy by transforming carbon dioxide from the air into simple carbohydrates. This stored chemical energy becomes the fuel for all life on earth. Water is also needed to provide essential elements, transport nutri- ents and sugars within plants, serve as a medium for essential chemical reactions, and provide structural form and strength by exerting turgor pres- sure from inside plant cells. Nutrient elements essential to the chemical reactions that occur within the plant are taken up from the soil through the roots. If nutrient elements or water are not adequately available at the time they are needed, plant growth and development will be affected. Growth and yield will be reduced or the plant may die. Plants need three soil-derived nutrient elements in large amounts nitro- gen, phosphorus, and potassium. These elements are frequently not avail- able in adequate amounts from soil. Nitrogen is a constituent of all proteins and a part of chlorophyll, the pigment that reacts to light energy. Nitrogen is a component of nucleic acids and the coenzymes that facilitate cell reac-

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142 ALTERNATIVE AGRICULTURE lions. Phosphorus, as a component of adenosine triphosphate (ATP), is critical to the development and use of chemical energy within the cell. Phosphorus is also a constituent of many proteins, coenzymes, metabolic substrates, and nucleic acids. Unlike nitrogen and phosphorus, potassium does not have a clear function as a constituent of chemical compounds within the plant. It is important in regulatory mechanisms affecting funda- mental plant processes, such as photosynthesis and carbohydrate translo- cation. In addition to these three nutrients, other soil-supplied nutrients are essential to plant growth and development: boron, calcium, chlorine, cobalt, copper, iron, magnesium, manganese, molybdenum, sulfur, and zinc. These elements are needed in small amounts that are often available . In SOI ,. Soil Properties anti Plant Nutrients Soil Texture The mineral particles that make up the soil are classified on the basis of their size. Clay particles are the smallest, silt is intermediate, and sand particles are the largest. The relative proportions of clay, silt, and sand determine soil texture. Soil texture has a critical influence on water and nutrient retention and movement through the soil. The large pores among grains of sand in a sandy soil allow water to pass through with relative ease, whereas the small pores formed in clay soils slow the flow and retain water. Soil particles can exist separately or they can be bound together in larger aggregates. Organic colloids and clays play a critical role in binding soil particles into soil aggregates, which increase pore space and water and air movement. Cation Exchange The molecular surfaces of clays and organic colloids have a net negative charge that interacts with the polar charge of surrounding water molecules. This causes the colloids to bind with positively charged ions of elements (cations). Because cations have differing abilities to bind with soil colloids, one cation may displace another; this is referred to as cation exchange. Displacement depends on relative bond strength and relative concentration. The cation exchange capacity of a soil is an expression of the number of cation-binding sites available per unit weight of soil (Foth, 1978~. This ca- pacity has a significant effect on nutrient movement and availability and binding of pesticides in different soils. Because hydrogen ions are cations that compete with nutrient cations for exchange sites, soil acidity, which is a measure of hydrogen ion concentration, has a marked effect on which nutrient elements are bound and which are displaced.

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RESEARCH AND SCIENCE Soil Quality 143 The quality of agricultural soils is derived from their effectiveness as a medium that provides essential nutrients and water. Mineral elements in soil required for plant growth exist in soluble and insoluble forms, which affects their availability for plant uptake. For example, under acidic or alka- line soil conditions, phosphorus fertilizer is rapidly converted into less soluble compounds that may be nearly unavailable for plant nutrition. Even available forms of phosphorus are bound to clay, and organic soil com- pounds and are relatively immobile in the soil profile except as a passenger during soil erosion. In contrast, potassium ant! the ammonium and nitrate forms of nitrogen are more soluble than phosphorus. Nitrate ions are not held by negatively charged soil ant! are readily leached. Because of their positive charges, potassium and ammonium nitrogen are held on the cation exchange and will not leach appreciably except through sandy soils. Organic matter in soils influences plant growth in a number of ways. The greatest benefits of organic matter in soil are its water-holding capacity; the manner in which it alters soil structure to improve soil filth; its high ex- change capacity for binding and releasing some mineral nutrients; its pres- ence as a food source for soil microbiota that recycle soil nutrients; and its mineralization to nitrogen, phosphorus, and sulfur. The cycling of mineral nutrients between living organisms and dead organic components of the soil system provides an important reservoir of the elements needed in plant growth. Nutrients are lost from soil through removal by crops, leaching, and soil erosion. Nitrate nitrogen can also be lost from the soil by conversion to nitrogen gases (denitrification) or by volatilization of ammonia. Gaseous loss of sulfur can also occur. Some farming practices help to mitigate the loss of nutrients and in some cases replace nutrients. For example, crop rotations that include nitrogen-fixing legumes benefit the soil in several ways. Legumes, in symbiotic relationships with microbes, fix atmospheric nitrogen into nitrogen compounds available for plant nutrition. When le- gumes are plowed under as green manures, they add nitrogen and organic matter to the soil. Cover crops help hold nitrogen in the root zone during the winter. The accumulated scientific knowledge on the role and fate of mineral elements, organic matter, ant! water in crop growth provides some indica- tion of why some alternative farming practices succeed and others fail. Characteristics of a particular crop or farming system that yield maximum efficiency are not well understood, however. The task remains to assemble the interdisciplinary expertise needed to analyze and understand the com- plex relationships that contribute to the relative efficiencies of different farming systems. Nutrient Management The adequate supply of nutrients particularly nitrogen, phosphorus, and potassium and maintenance of proper soil pH are essential to crop growth.

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144 ALTERNATIVE AGRICULTURE Ideally, soil nutrients should be available in the proper amounts at the time the plant can use them; this avoids supplying an excess that cannot be used by plants and may become a potential source of environmental contamina- tion. The current conventional approach is to apply nutrients in the form of fertilizers at levels needed for maximum profitability. Profitability in the context of current government programs has generally been achieved, how- ever, through maximum yield per acre, often in continuous cropping or short rotations that require significant amounts of fertilizer. The nutrients in any excess fertilizer or high levels of decomposing organic matter are subject to leaching or runoff. An alternative, more environmentally benign approach to nutrient man- agement is to reduce the need for fertilizer through more efficient manage- ment of nutrient cycles and precise applications of fertilizer. Such practices include application of organic waste residues from animals and crops, crop rotations with legumes, improved crop health that may result in better use of nutrients, and banded or split applications of fertilizers. In mixed crop and livestock operations, for example, many of the nutrients contained in the grain and residue from crops grown on the farm can be returned to the soil if the manure and crop residues are incorporated into the soil. Crop rotations that include legumes can also play an essential role in nutrient cycling, particularly for replenishing the nitrogen supply. Plant residues and manure can release nitrogen more continuously throughout the growing season than can common commercial fertilizers. However, nitrogen from organic sources may be released when crops are not actively absorbing it. In contrast, inorganic fertilizer nitrogen is relatively quickly converted to the soluble and leachable nitrate form. Efforts to provide adequate nutrition to crops continue to be hindered by inadequate understanding and forecasting of factors that influence nutrient storage, cycling, accessibility, uptake, and use by crops during the growing seasons. Soil testing and plant tissue analysis can provide the farmer with information to assure adequate nutrition for all agronomic and horticultural crops. But variable soil and climatic conditions that influence nutrient up- take and Toss make it difficult to predict the most profitable and environ- mentally safe levels of nutrients. As a result, farmers often follow broad guidelines that lead to insufficient or excessive fertilization. For example, ~ . ~ ~ .~ . ~ . . ~ ~ . ~ . ~ _ 1 _ _ _1 studies of tertlllzer recommendations revealed tnat some commercial So testing services consistently recommended the use of far more fertilizer than was needed (Olson et al., 1981; Randall and Kelly, 19871. Additionally, some farmers apply more nitrogen than is recommended. Nitrogen Nitrogen is the soil-derived plant nutrient most frequently limiting grain production in the United States. This is ironic because the atmosphere is 79 percent nitrogen by volume. Atmospheric nitrogen is in the form of inert nitrogen gas, however, which higher-order plants cannot use. Converting

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RESEARCH AND SCIENCE 145 atmospheric nitrogen to ammonia and other forms that plants can use requires a high energy input. This is true for biological nitrogen fixation as wed as industrial synthesis. The biological process is fueled by photosyn- thates; the synthetic industrial process is fueled by natural gas, petroleum, coal, or hydroelectric power. The predominant process for producing syn- thetic nitrogen fertilizers involves combining hydrogen from methane gas and atmospheric nitrogen at high temperature and pressure to form am- monia. Ammonia can then be converted to nitric acid or combined with other elements to form a number of nitrogen fertilizers, including ammo- nium nitrate, ammonium sulfate, ammonium phosphate, and urea. A sig- nificant amount of energy is required to synthesize ammonia. Conse- quently, energy and methane gas costs can affect the availability and cost of synthetic nitrogen fertilizers. Neutral ammonia molecules gain a hydrogen ion when added to moist soil and become stable ammonium ions with a net positive charge. Most of the ammonium ions in soil undergo biological Vitrification, in which oxida- tion results in the formation of a nitrate ion as well as hydrogen ions that acidify the soil. Because ammonium ions have a positive charge, they are adsorbed and held on the soil cation exchange. Nitrate ions, because of their negative charge, are not adsorbed on the soil exchange complex. While readily available for plant use, the nitrate freely moves through soil in water unless it is absorbed by the plant. Although these basic processes are understood, there is a need to know much more about nutrient cycling and the behavior of nitrogen under various environmental conditions. To accomplish this, progress is needed in estimating the rates of biological reactions that control nitrogen transfor- mation in soil. .. . . , . . . . - _ - ~ . ~ . Legumes as a Source of Nitrogen Nitrogen can be provided by growing legumes in rotation with grains. For alternative farming, legumes are an effective and often profitable way to supply nitrogen. Leguminous nitrogen is consistently released through- out the growing season when temperatures are high enough to permit microbial decomposition. Combiner! with the rotational effect, leguminous nitrogen can support high yields of corn and wheat (Holben, 1956; Koerner and Power, 1987; Voss anct Shrader, 1984~. The overall contribution of leg- umes, however, depends on the management system and climate. For ex- ample, forage legumes are most effective in humid and subhumid regions (Meisenbach, 1983; U.S. Department of Agriculture, 1980~. In regions with less than 20 inches of rain a year, deep-rooted, nonirrigated legumes may decrease subsoil moisture and lead to reduced corn yields the following year (Meisenbach, 1983~. The profitability of leguminous hay crops is strongly influenced by the presence of on-farm livestock or a local hay market. Legumes supply substantial nitrogen to the soil, but the amount of nitro- gen fixed is highly variable. Different species and cultivars fix different

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184 ALTERNATIVE AGRICULTURE For a variety of reasons, most plant diseases cannot be directly controlled. For example, many of the fungi that infect plant roots have not been fully investigated, nor has their importance in affecting yield been quantified. In most cases, farmers cope with diseases by using good farm management practices and planting resistant varieties. When combined with the existing natural level of biological control, management and resistant varieties keep the majority of diseases in check. Nonetheless, disease can still cause sig- nificant yield loss. Moreover, germplasm for desirable resistance has not been identified for many of the worId's important crops. More research is needed to better characterize available germplasm for genetic resistance to disease and plant transformation. The development and durability of resistant varieties have been a chal- lenge to plant pathologists and plant breeders. Genetic strategies to im- prove the durability of resistance include use of multilines and cultivar mixtures as well as multigenic or horizontal resistance. Modern genetic technology will speed the development of resistant crops. It should be possible to identify genes that confer resistance to a specific pathogen. These genes would then be introduced to the appropriate plant, without incorporating other genes that may confer detrimental characteristics. This gene transfer has been achieved to produce resistance to several plant vi- ruses in tobacco plants (National Research Council, 1987a). Advances in understanding the genetic and molecular bases of disease in plants promise major improvements in plant disease control using genetic rather than chemical methods (Goodman, 1988~. Cultural practices such as crop rotations, alteration of soil pH, sanitation, and adjustment of the timing of planting and harvest to avoid peak periods of the pathogens complement genetic resistance in many situations. For example, raising soil pH with lime from 6.5 to 7.5 reduces the severity of fusarium wilts on tomato and potato crops in Florida (Jones and Woltz, 1981~. Lowering soil pH with sulfur to 5.0 controls potato scab caused by Streptomyces scabies (Oswald and Wright, 19501. Forms of nitrogen also can play a significant role in disease severity. For example, ammonium nitrogen suppresses the disease take-all in wheat but nitrate favors it (Huber et al., 1968~. Tillage practices can have effects on pathogen populations and resultant diseases. Ecofallow is a form of conservation tillage that can reduce stalk rot of sorghum but permits increases in other diseases (Cook and Baker, 1983~. Harvesting and processing practices can also influence the inception of disease. The hydrostatic pressure from tank-washing potatoes causes water infiltration of pathogens into the lenticels of the tubers, predisposing them to attack by bacterial soft rot (Bartz and Kelman, 1985~. Potatoes are then generally treated with a fungicide. There is enormous need and potential to control diseases by nonchemical methods (Cook and Baker, 1983~. But there remains a lack of understanding of the underlying mechanisms that affect disease incidence and severity.

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RESEARCH AND SCIENCE 185 Synthetic chemical control of plant pathogens has become an increasingly important pest control tactic as agriculture has shifted toward intense cul- tivation of monocultures (Delp, 1983~. Practices previously used to control pathogens, such as crop rotations, are not compatible with current crop specialization (Tweedy, 1983~. Because commercial cultivars are genetically related, the loss of resistance to pathogens could cause serious problems if fungicides were not available. In California, the use of methyl bromide and chloropicrin soil fumigation resulted in huge increases in yield and quality in several crops (Wilhelm and Paulus, 1980~. This combination is widely credited with saving the strawberry industry from high production costs and foreign competition. Although the total amount of fungicides used in the United States is much less than the amount of herbicides or insecticides, the potential chronic health risk to humans is significant. Ninety percent (by weight) of fungicides applied are known to cause tumors in laboratory animals. Fun- gicicle residues in food are responsible for the largest share of potential dietary oncogenic risk from pesticides. Developing fungicides not toxic to nontarget organisms, including humans, is difficult; very few new fungi- cides have reached the market. Only four nononcogenic fungicides have been introduced in the past 15 years that have captured greater than 5 percent of any food crop market (National Research Council, 1987b). In recent years, there has been a movement toward the development of highly specific systemic fungicides, but this has accelerated evolutionary selection of fungicide-resistant plant pathogens. Research to understanc! the mecha- nisms of resistance could aid the development of chemicals with new modes of action ant! better-targeted effects. The introduction or application of biological control agents has not been very successful with plant pathogens because of the great complexity in microbial communities. Although many of the management practices that indirectly control diseases strike a balance between beneficial and deleteri- ous microorganisms, there is insufficient knowledge to effectively develop and use biological control agents commercially (Schroth and Hancock, 19851. Little is known concerning the ecology, classification, and physiology of biological control organisms or the underlying mechanisms affecting the interactions among beneficial microorganisms, pathogens, and plants. The potential to use microorganisms against microorganisms has stirred the interest of many investigators. A number of companies have pioneered efforts to develop biological control agents for plant pathogens. Several products have already reached) the market. An avirulent, antibiotic-produc- ing strain of Agrobacterium is available to control crown gall tumors of orna- mental plants and orchard trees caused by Agrobacterium tumefaciens (National Research Council, 1987a). Plans are underway to market a root- colonizing Pseudomonas bacterium as a control for Rhizoctonia and Pythium fungi in cotton. Another interesting disease control possibility is to stimulate a plant's own defense system with chemicals or by inoculation with an avirulent

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186 ALTERNATIVE AGRICULTURE form of a pathogen. The citrus tristeza virus from Africa entered Brazil in the 1920s and nearly decimated the citrus industry. In the 1950s, researchers found a mild strain of the virus that protected trees from the severe strain. Commercial inoculation with the mild virus began in the late 1960s and has been very successful so far (National Research Council, 1987a). It remains unlikely, however, that disease control in continuous crop monocultures in certain regions, such as fruit and vegetable production in the East and Southeast, will be possible without use of synthetic chemical fungicides and fumigants. Disease pressures in areas with high temperatures and humid*y and long growing seasons are so severe that only dramatic changes in production systems will enable widespread adoption of alternative dis- ease control measures. Alternative Nematode Control Nematode control is particularly difficult. Strategies include genetic resis- tance, chemical control, and cultural methods such as rotations (see the BreDahT, Kutztown, Thompson, and Kitamura case studies). Genetic resis- tance is successful in only a few cases. Chemical control, which is feasible only in certain situations, relies on broad-spectrum, highly toxic, and often volatile materials. It is expensive and hazardous. The decline of basic cul- tural practices such as rotations, particularly in the Midwest, has led to an increase in nematodes in soybeans. Rotating corn with soybeans will control most nematode problems. Current research for nematode control is focusing on the development of effective cultural practices such as those traditionally practiced before the advent of broad-spectrum nematocides. Genetic research to develop nematode-resistant cultivars has been suc- cessfuT in sugar beets and tomatoes (Goodman et al., 19871. More research is necessary to determine how various nematodes damage different crops and how to modify practices if a combination of nematode species is pres- ent. Similarly, the accuracy and efficiency of techniques for estimating nem- atode populations needs to be improved. The biological antagonism level of the soil must be determined if manage- ment decisions are to be based on an understanding of the relationship between yield and population density of nematodes. A given number of nematodes will affect the same crop differently in soils of differing biota. More basic studies in biological control and interactions in the rhizosphere are required. Improved assay techniques for assessing the biological antag- onism coefficients of various soils must be developed. One promising biological control agent is the pathogenic bacterium Pas- teuria penetrans, which is effective against several economically important nematodes. It is expensive to produce on a large scale, however. A less expensive, but also less effective, biological control option is the use of plants such as CrotaZaria spectabilis that prevent the nematode from repro- ducing. Coastal Bermuda grass (Cynodon daclylon) incorporated before planting lespedeza, tobacco, or vegetable transplants protects against root-

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RESEARCH AND SCIENCE 187 knot nematodes (Meloidogyne spp.) (Burton and Johnson, 1987). Coastal Bermuda grass will also reestablish itself after the annual crop is harvested. These plants could be even more effective if they could be genetically engineered to produce nematode attractants or pheromones. The selection and development of varieties for resistance and tolerance to nematode stress will continue. This may involve incorporation of appropri- ate genetic material into varieties already selected for production, economic, and marketing qualities. It is still important to develop biological and chem- ical nematocides that are systemic, easily associated with the root system, target organism specific, or a combination of these factors. These pesticides will allow flexibility in management decisions and compensation for man- agement errors that have promoted or amplified nematode stress problems in a particular production system. Alternative Weed Control Farmers in the United States depend greatly on herbicides to control weeds. Nearly two-thirds of U.S. pesticide purchases are for herbicides. But a variety of other means, such as crop rotations, mechanical cultivations, competition with other plants, and biological control through natural ene- mies can control weeds (see Spray, BreDahI, Sabot Hill, Kutztown, Thomp- son, Pavich, and Lundberg case studies). In fact, growers are often unaware of the forces naturally controlling weeds. The purslane sawfly and the leafmining weevil, for example, help control pursTane in California. These insects would be even more effective if their populations were not reduced by insecticide use. The moth Bactra verutana suppresses the weed Cyperus rotundus that infests cotton in Mississippi. More than 70 plant-feeding in- sects and plant pathogens have been introduced to control weeds in the United States; 14 weed species are now controlled in this way (National Research Council, 1987a; Osteen et al., 1981). Few weeds are controlled biologically in agriculture, however, although future opportunities are nu- merous. For example, many of the hundreds of species of carabid beetles are seed eaters and could play a role in weed control (Andres and Clement, 1984). Cultural practices are currently the most effective alternative to herbi- cides. Cultivating, rotary hoeing, increasing the density of the crop plant to crowd out weeds, intercropping, timing of planting to give the crop a competitive advantage, and transplanting seedling crop plants to give them a head start on weeds are currently practiced and effective measures. Trans- planting tomatoes to a high density has successfully controlled the growth of shade-intolerant redroot pigweed. Clover planted as an understory or living mulch reduces weed growth in corn. Several combinations of cover crops and tillage practices are effective in controlling weeds in corn and soybeans. Weed-tolerant crops and crops that produce substances toxic to weeds are potentially promising approaches that have received little research atten-

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188 ALTERNATIVE AGRICULTURE lion. Naturally occurring phytotoxic allelopathic chemicals, however, may not always be safer than some of the more undesirable synthetic herbicides. Introducing weed diseases is also a possibility. The rust Puccinia chondriZZina controls the rush skeleton weed, which is a problem in wheat and pasture areas. AZternaria macrospora can inhibit the growth of spurred anode, a damaging weed in cotton production that is resistant to several cotton herbicides. The development of herbicide-resistant crops may offer opportunities to substitute safer herbicides for more dangerous herbicides. For example, efforts are being made to develop crops resistant to the herbicide glyphos- ate, a compound with very low mammalian toxicity. Like other broad- spectrum herbicides, glyphosate has limited use in crop production because it destroys crops as well as weeds and therefore must be used before crop germination or with special application methods and equipment. In re- sponse to this problem, researchers have isolated glyphosate-resistant genes and successfully transferred them to poplar trees, tobacco, and tomatoes (Della-Croppa et al., 1987; Stalker et al., 1985~. If the plants tolerate gly- phosate, the herbicide could then be used as a postemergent treatment. In certain cases, this strategy could reduce weed control costs, improve weed control quality, and reduce human health hazards. SUMMARY Alternative farming encompasses a range of farming practices, including the use of crop rotations, IPM, biological and cultural pest control, use of organic materials to enhance soil quality, different tilIage methods, and animal rearing techniques that involve less reliance on antibiotics and con- finement. The unifying premises of alternative systems are to enhance and use biological interactions rather than reduce and suppress them and to exercise prudence in the use of external inputs. Research has not fully addressed the integration of study results essential to the adoption of a number of alternative farming methods as unified systems. Although some components of alternative systems have been ex- amined, they have been generally studied in isolation. Lack of systems research is a key obstacle to the adoption of a number of alternative farming practices. On the whole, land-grant universities and the USDA have not adequately integrated the results of this research into production systems. Nonetheless, a significant amount of scientific evidence exists that sup- ports the effectiveness of a range of alternative practices. There is a large body of information about the value of legumes in fixing nitrogen, improv- ing soil quality, reducing erosion, and increasing yields of subsequent crops. {PM programs are effective, profitable, and increasingly adopted. Although biological and natural controls are underused, they have been demonstrated to be effective and warrant increased research support. Genetic engineering techniques should enhance this aspect of IPM. The integration of livestock

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RESEARCH AND SCIENCE 189 into farming systems provides additional means for nutrient cycling. Im- proving forage digestibility needs further research, however. The scientific basis for some of these practices and their interaction in agricultural systems is not always understood, but they work. Many farmers have adopted them and are using them profitably. The economics of these and other alternative farming practices and systems are discussed in the following chapter. REFERENCES Allen, W. A., E. G. Rajotte, R. F. Kazmierczak, Jr., M. T. Lambur, and G. W. Norton. 1987. The National Evaluation of Extension's Integrated Pest Management (IPM) Programs. VCES Publication 491-010. Blacksburg, Va.: Virginia Cooperative Extension Service. Alrawi, A. A., R. C. Laben, and E. I. Pollack. 1979. Genetic analysis of California mastitis test records. II. Score for resistance to elevated tests. Journal of Dairy Science 62:1105-1131. Amstutz, H. E., ed. 1980. Bovine Medicine and Surgery, 2d ed. Santa Barbara, Calif.: Ameri- can Veterinary Publications. Anderson, D. P., W. R. Pritchard, l. l. Stockton, W. G. Bickert, L. Bohl, W. B. Buck, J. Callis, R. Cypess, l. Egan, D. Gustafson, D. Halvorson, B. Hawkins, A. Holt, A. D. Leman, S. W. Martin, T. D. Njaka, B. I. Osburn, G. Purchase, W. W. Thatcher, H. F. Troutt, l. Williams, and R. G. Zimbelman. 1980. Animal health. Pp. 129-151 in Animal Agriculture Research to Meet Human Needs in the 21st Century, W. G. Pond, R. A. Merkel, L. D. McGilliard, and ]. Rhodes, eds. Boulder, Colo.: Westview Press. Andraski, B. J., D. H. Mueller, and T. C. Daniel. 1985. Phosphorus losses in runoff as affected by tillage. Soil Science Society of America lournal 49:1523-1527. Andres, L. A., and S. L. Clement. 1984. Opportunities for reducing chemical inputs for weed control. Pp. 129-140 in Organic Farming: Current Technology and Its Role in a Sustainable Agriculture, Special Publication No. 46, D. F. Bezdicek and J. F. Power, eds. Madison, Wis.: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America. Baker, K. F., and R. ]. Cook. 1982. Biological Control of Plant Pathogens. St. Paul, Minn.: American Phytopathological Society. Baker, T. C., R. T. Staten, and H. M. Flint. In press. Use of pink bollworm pheromone in the southwestern United States. In Behavior-Modifying Chemicals for Insect Management: Applications of Pheromones and Other Attractants, R. L. Ridgway, R. M. Silverstein, and M. N. Inscoe, eds. New York: Marcel Dekker. Baldani, V. L. D., l. I. Baldani, and l. Dobereiner. 1987. Inoculation of field-grown wheat (Triticum aestivum) with Azospirillum in Brazil. Biology and Fertility of Soils 4:37-40. Balfour, E. B. 1976. The Living Soil and the Haughley Experiment. New York: Universe Books. Barnes, D., G. Heichel, and C. Sheaffer. 1986. Nitro alfalfa may foster new cropping system. News, November 20. St. Paul, Minn.: Minnesota Extension Service. Bartz, ). A., and A. Kelman. 1985. Infiltration of lenticels of potato tubers by Erwinia carotovora pv. carotovora under hydrostatic pressure in relation to bacterial soft rot. Plant Disease 69:69-74. Bennett, R. H. 1987. Milk quality management is mastitis management. Pp. 133-150 in Proceedings of the 26th Annual Meeting of the National Mastitis Council, Inc. Arlington, Va.: National Mastitis Council. Blaser, R. E., R. C. Hammes, Jr., J. P. Fontenot, and H. T. Bryant. 1980. Forage-animal systems for economic calf production. Pp. 667-671 in Proceedings of the XIII International Grass- land Congress. Berlin: Akademie-Verlag. Booth, W. 1988. Revenge of the "nozzleheads." Science 23:135-137. Burton, G. W., and A. W. Johnson. 1987. Coastal Bermuda grass rotations for control of root- know nematodes. lournal of Nematology 19:138-140.

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190 ALTERNATIVE AGRICULTURE Chalupa, W. 1980. Chemical control of rumen microbial metabolism. Pp. 325-347 in Digestive Physiology and Metabolism of Ruminants, Y. Ruckebusch and P. Thivend, eds. Lancaster, England: MTP Press Limited. Coleman. D. C.. C. P. P. Reid. and C. V. Cole. 1983. Biological strategies of nutrient cycling in soil systems. Advances in Ecological Research 13:1-55. Coleman, D. C., C. V. Cole, and E. T. Elliott. 1984a. Decomposition, organic matter turnover, and nutrient dynamics in agroecosystems. Pp. 83-104 in Agricultural Ecosystems: Unify- ing Concepts, R. Lowrance, B. R. Stinner, and G. I. House, eds. New York: Wiley/ Interscience. Coleman, D. C., R. E. Ingham, J. F. McClellan, and J. A. Trofymow. 1984b. Soil nutrient transformation in the rhyzosphere via animal-microbial interactions. Pp. 35-38 in Inver- tebrate-Microbial Interactions, J. M. Anderson, A. D. M. Rayner, and D. W. H. Walton, eds. Cambridge, England: Cambridge University Press. Cook, R. l. 1984. Root health: Importance and relationship to farming practices. Pp. 111-127 in Organic Farming: Current Technology and Its Role in a Sustainable Agriculture, Special Publication No. 46, D. F. Bezdicek and J. F. Power, eds. Madison, Wis.: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America. Cook, R. J. 1986. Wheat management systems in the Pacific Northwest. Plant Disease 70(9):894-898. Cook, R. l., and K. F. Baker. 1983. The Nature and Practice of Biological Control of Plant Pathogens. St. Paul, Minn.: American Phytopathological Society. Council for Agricultural Science and Technology. 1980. Organic and Conventional Farming Compared. Report No. 84. Ames, Iowa. Council for Agricultural Science and Technology. 1981. Antibiotics in Animal Feeds. Report No. 88. Ames, Iowa. Council for Agricultural Science and Technology. 1986. Forages: Resources for the Future. Report No. 108. Ames, Iowa. Crowder, B. M., D. J. Epp, H. B. Pionke, C. E. Young, J. G. Beierlein, and E. J. Partenheimer. 1984. The Effects on Farm Income on Constraining Soil and Plant Nutrient Losses: An Application of the CREAMS Simulation Model. Research Bulletin 850. University Park, Pa.: Agricultural Experiment Station, Pennsylvania State University. Dabney, S. M., G. A. Breitenbeck, B. I. Hoff, J. L. Griffin, and M. R. Milam. 1987. Manage- ment of subterranean clover as a source of nitrogen for a subsequent rice crop. Pp. 54-55 in The Role of Legumes in Conservation Tillage Systems, J. F. Power, ed. Ankeny, Iowa: Soil Conservation Society of America. Della-Croppa, G., S. C. Bauer, M. L. Taylor, D. E. Rochester, B. K. Klein, D. M. Shah, R. T. Fraley, and G. M. Kishore. 1987. Targeting a herbicide-resistant enzyme from Escherichia cold to chloroplasts of higher plants. BiolTechnology 5:579-584. Delp, C. 1983. Changing emphasis in disease management. Pp. 416-421 in Challenging Problems in Plant Health, T. Kommendahl and P. H. Williams, eds. St. Paul, Minn.: American Phytopathological Society. Eggert, F. P., and C. L. Kahrmann. 1984. Response of three vegetable crops to organic and inorganic nutrient sources. Pp. 97-109 in Organic Farming: Current Technology and Its Role in a Sustainable Agriculture, Special Publication No. 46, D. F. Bezdicek and J. F. Power, eds. Madison, Wis.: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America. Elliott, L. F., R. I. Papendick, and D. F. Bezdicek. 1987. Cropping practices using legumes with conservation tillage and soil benef*s. Pp. 81-90 in The Role of Legumes in Conservation Tillage Systems, J. F. Power, ed. Ankeny, Iowa: Soil Conservation Society of America. Forsberg, C. W., B. Crosby, and D. Y. Thomas. 1986. Potential for manipulation of the rumen fermentation through the use of recombinant DNA techniques. Journal of Animal Science 63:310-325. Foth, H. D. 1978. Fundamentals of Soil Science, 6th ed. New York: Wiley. Freedeen, H. T., and B. G. Harmon. 1983. The swine industry: Changes and challenges. Journal of Animal Science 57(Suppl. 2~:110-118.

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