Making the Transition to Sustainable Farming

Fundamentals of Sustainable Agriculture

Appropriate Technology Transfer for Rural Areas (ATTRA)
P.O. Box 3657
Fayetteville, AR 72702
Phone: 1-800-346-9140 --- FAX: (501) 442-9842

Index
Introduction
Planning and Decision Making
Rotations and Cover Crops

Developing a Cropping Mix
The Important of Sod in Rotation
Cover Crops & Green Manures

Weed Management
Insect Pest Management
Plant Disease Management

Sustainable farming is a management-intensive method of growing crops at a profit while concurrently minimizing negative impact on the environment, improving soil health, increasing biological diversity, and controlling pests.  Sustainable agriculture is dependent on a whole-system approach having as its focus the long-term health of the land.  As such, it concentrates on long-term solutions to problems instead of short-term treatment of symptoms.  One result of such a strategy is that use of agricultural chemicals and similar inputs is reduced, though not necessarily eliminated.   As a consequence, the land develops diversity and resiliency that further reduce the need for agricultural chemicals.

It is widely agreed that a truly sustainable farm system must be sustainable economically, ecologically and socially:

To be economically sustainable, farms should generate sufficient equitable returns to support farm families and to provide an economic base for the surrounding community.

To be ecologically sustainable, farming methods must be modeled on nature to foster  energy flow, effective water and mineral cycles, and viable community dynamics.
 

• Energy flow is enhanced through increased  capture of solar energy and strategies to  effectively utilize and store it. Off-season  cover crops, perennial vegetation and relay  planting are among the tools for capturing  more sunlight; feeding livestock on-farm and  carefully managing soil organic matter are  means of conserving and storing it.  Strategies that conserve fossil-based fuels  and/or substitute renewable energy sources also contribute positively to energy flow.
  
  
• Water cycling is improved through  strategies and techniques that prevent  erosion, increase the infiltration and water-holding potential of the soil, and  reduce contamination of water resources  by pesticides, fertilizers, and suspended  matter.
  
  
• The mineral cycle is fostered by the cycling and recycling of wastes on-farm.   On-farm feeding of livestock is especially useful, as is the careful management of crop residues, the use of catch crops to reduce  leaching losses, and practices that prevent  wind and water erosion.
  
  
• Effective community dynamics is encouraged through increased biodiversity. Crop rotation, companion planting, strip  cropping, and the integration of livestock  and crop enterprises are all means of increasing farm biodiversity.   Community dynamics is also enhanced by the  appropriate introduction of perennial crops and trees where possible.
  
  

Sustainable agriculture is neither high technology nor low technology, rather it is appropriate technology; and unlike the conventional approaches of the late 20th century it varies considerably with each farm and farmer.  In place of the prescriptions characteristic of conventional agriculture, the modern farmer has access to descriptions of new, innovative, and highly effective approaches that can be applied to virtually any farm situation from micro-scale vegetable growers to large-scale cash crop farmers.

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Planning And Decision Making

Because sustainable producers are much more sensitive to the complexity of healthy natural systems, effective management depends on clear goal-setting and effective decision making.

Several useful processes for decision making, goal formation, and whole farm management have been developed. The Kerr Center for Sustainable Agriculture, for example, has developed 10 criteria for wholistic evaluation of farming systems (1).  A more comprehensive approach called Holistic Management® is more widely known and practiced, however.  Both processes (and others like them) guide the farmer through an evaluation procedure to test the suitability of tools and enterprises for the operation.

One key element of success in the transition to sustainable farming is the farmer's ability to monitor both progress towards the goal and the overall health of the system.  It is advisable to assume that one's plan will not work and develop a system for determining (as soon as possible) if indeed it isn't working.  For example, if the goal includes increased biodiversity, the farmer needs to know—quickly—if the grazing management system being used is actually decreasing the number of plant species per acre; or if hiring a neighbor to combine grain is more economical than personal combine ownership.

The ability to evaluate and replan is a vital tool for the farmer wishing to become more
sustainable.  When part of the plan is not working as intended, it becomes necessary to replan and reflect the new conditions.  This concept—the idea of planning - monitoring - controlling - replanning — is a key characteristic of Holistic Management and is referred to as the feedback loop.

An international organization, the Center for Holistic Management, has several publications on Holistic Management, and offers a series of courses that may be quite helpful to farm families moving towards sustainable farming (2).

The transition towards more sustainable farming requires not only more responsibility for decision making on the part of the farmer, but also access to appropriate and helpful information.  Fortunately, increased interest in sustainable agriculture has stimulated greater investment in research and education.  As a result, much more usable information is available today than ever before.  Access to this information can be made through various means, one of them being ATTRA.  In addition to its publications and custom reports on production and marketing, ATTRA also provides resource lists covering sustainable agriculture organizations, educational programs, internships, and related resources.  Please consult the ATTRA Materials List for a detailed publications listing.

Hiring a consultant can also pay off well, especially in the early years of transition.  A study by Iowa State University Extension (3) reports that 59% of farmers hiring a consultant reported an increase in profits and attributed that increase to their consultant.  However, be certain to check credentials and ask for references before making a commitment.

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Rotations And Cover Crops

Crop rotation, the planned sequencing of crops over time on a field, is one of the cornerstone techniques of sustainable farming.  Rotating crops diversifies farm income, increases the biodiversity of the farm organism both within and on top of the soil, breaks many weed and other pest life cycles, improves nutrient cycling and utilization—especially where legumes are used to fix nitrogen—and provides the opportunity for soil building where sod crops are employed.

Crop rotation improves overall soil health and increases farm system diversity through time and across space.  Good rotations are sufficiently long and diverse to minimize pressure from weeds, insects, and diseases.  Whereas conventional production seeks to maximize the productivity of an individual crop with agricultural chemicals, the sustainable approach makes the whole system more productive through creative use of biodiversity and recognition of new profit opportunities.

Developing a new rotation cropping mix—one that allows for soil building—requires that some land be used to grow crops that appear less profitable in the short term.  This may be especially challenging on high-priced land and will, in any case, have a noticeable impact on cash flow; if expenses do not decrease at least as much as income decreases, there will also be a negative impact on net income.  Therefore, careful planning is essential to avoid negative results.

In planning rotation options it is also important to consider that cultivated row crops, such as corn and beans or vegetables, tend, by their nature, to be soil-degrading crops—especially in warmer climates.  Since the soil is open and cultivated between rows, microbes break down soil 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.  A continuous CORN-BEAN-CORN-BEAN "rotation" can, therefore, lead to soil degradation similar to that found in systems of continuous corn production.  Cropping continuous vegetables has a roughly similar effect.

A noteworthy challenge in sustainable row-crop production is that reduction of herbicide use may lead to increased tillage (for weed control).  Unless great care is taken, this may actually result in a loss of organic matter comparable to that of similar conventional systems.  Consequently, it is important to develop production systems that reduce tillage in a manner consistent with effective weed control.  Careful timing, for example, can substantially reduce the number of cultivations required each season.

Management of soil organic matter is especially important in sustainable systems— particularly where row cropping is involved.  One recent study (4), for example,  has shown that in sandy soils, raising soil organic matter from 1% to 2% increased the available water content of that soil by 60% (from 5% of total soil volume to 8%).  Such an improvement in a soil's water-holding capacity will have a beneficial effect on crop growth, especially during droughty periods.

Cereals and other crops (such as annual green manures) planted with a grain drill or broadcast-seeded are more closely spaced and have more extensive root systems than do row crops, greatly reducing the amount of soil exposed to degradation.  In addition, they 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, producing far more organic matter than is lost.  Sod crops are the most effective soil-building crops—making a major contribution by healing the damage done to soil by row cropping.

Conscientious producers incorporate sod crops as a fundamental part of their rotation, not only to build soil, but to buttress weed control strategies. Weed control improves because the types of weeds encouraged by row cropping systems are usually not adapted to growing in a sod/hay crop.  An ideal rotation might include one year of sod crop for each year of row crop, and as many years of neutral crops as makes sense in the circumstances.  A common example among sustainable cash crop/livestock farmers is the CORN-BEANS-OATS-ALFALFA-ALFALFA rotation.
 
Many farmers (5,6,7) report the best results from focusing on legume sod crops early in the transition process; after several years of soil-building, more grasses are planted to prevent the system from becoming too rich in nitrogen.

The chief challenge of incorporating sod crops into a rotation is to include livestock in the system or to find a market for the hay.  Sustainable production is much easier when livestock are present in the system to recycle wastes and assist in transferring (via manure) nutrients from one part of the farm to another. Fortunately, land capable of producing a 100-bushel corn yield will generally be able to produce 5-ton hay yields.  At the $60-$70 per ton prices common for even fairly ordinary hay, gross revenues per acre from hay will exceed those from corn so long as corn is under $3.00 per bushel.  The net income picture is even more encouraging, however, because conventional production costs for an acre of corn are quite a bit higher than for hay.  A good crop of alfalfa fixes at least $50 of nitrogen every year, and by thus reducing fertilizer costs for the subsequent corn crop, the net income for that crop is improved also.

Besides equipment costs, the major drawback to selling hay is that the nutrients it contains are shipped off the farm.  Since, however, something like 75–90% of the minerals going into the front end of cattle come out the back end, keeping cattle helps retain nutrients on the farm.  Cattle can serve as a very profitable method of adding value to the forage crops they consume; and when new high tensile electric fencing is employed, the costs of marketing forage as meat are not prohibitive.

Since row crop farmers are often reluctant to plant perennial and biennial sod crops, annual green manures and cover crops assume an important role in soil building in field cropping systems.  Hairy vetch, for example, is not only a soil-conserving cover crop, but is capable of providing all the nitrogen required by subsequent crops like commercial tomatoes (8).

The soil-building crops most appropriate for a given farm depend not only on regional factors (harshness of winter, etc.) but also on the type of production system involved: each farmer will have to determine which cover crops are most appropriate to his or her system.  The ATTRA publication entitled Cover Crops and Green Manures, which may help in cover crop evaluation, is available upon request.

Planned crop rotations, cover cropping and green manuring are key elements in soil building.  However, modern production systems place high demands on land resources, requiring additional attention to soil fertility management.  To better understand the basic concepts involved, ATTRA's Sustainable Soil Management publication is suggested.  It provides practical information about alternative soil management approaches.  Since some of these approaches may entail the use of various off-farm inputs, two additional ATTRA publications — Nonconventional Soil Amendments and Sources for Organic Fertilizers & Amendments — are recommended.

Manures and composts, especially those produced on-farm or available locally at low cost, are ideal resources for soil management.  From the standpoint of overall soil and crop health, composts or aged manures are preferred.  Compost has a unique advantage in comparison to unaged manure and other organic soil amendments in that it has a (usually) predictable, and nearly ideal, ratio of carbon to nitrogen (9).  As a result, there is no need to calculate the extra amount of nitrogen needed to balance the decay process, and farmers need not fear that soil nitrogen will be tied up by decaying residues.  Compost can safely be applied to row-crop ground at any practical rate; applications of 10 tons per acre (9) are common where quantities are available, but much higher rates are not unusual, especially when soil is being improved rather than maintained.

Compost has some particular advantages in row crop production, especially when used in conjunction with cover crops and green manures.  In sandy soils, compost's stable organic matter is especially effective at absorbing and retaining water.  Fresh plant material incorporated as green manure, on the other hand, retains its waxy leaf coating and cannot perform the same function until thoroughly digested by microbes.

Some of the more "environmentally friendly" chemical fertilizers such as mono-ammonium phosphate (12-50-0), commonly called MAP, may also have a role in the transition away from the harsher chemical fertilizers.  A very serviceable and affordable 4-16-16 transitional fertilizer with magnesium, sulfur, and other minor nutrients can be prepared from a combination of two-thirds sulfate of potash-magnesia and one-third mono-ammonium phosphate.  When used in combination with composts and/or legume plowdowns (for nitrogen), this 4-16-16 can be banded at seeding or otherwise applied just like the regular 5-20-20, but with reduced negative impact on soil life.

There are several conventional fertilizers that should be avoided in sustainable farming due to harmful effects on soil organisms and structure.  These include anhydrous ammonia and potassium chloride.  The use of dolomite ¾ a liming material having a high magnesium : calcium ratio ¾ has also been generally discouraged.  This results more from the frequent misuse of dolomite for raising pH on soils already high in magnesium, rather than innate detrimental qualities.  It is certainly appropriate for use on fields deficient in magnesium as indicated by proper soil tests.

Significant additions of lime, rock phosphate and fertilizers should be guided by soil testing to avoid soil imbalances and unnecessary expenditure on inputs.  Cooperative Extension offers low-cost soil testing services in many states.  For additional sources, ask for ATTRA's Alternative Soil Testing Laboratories publication.

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Weed And Pest Management

In the early years of transition towards sustainable production, farmers should expect significant fluctuations in pest and weed populations.  Farm chemicals and healthy farm systems each act as powerful dampers on the population swings of "problem organisms."   However, during the period between reduction of chemical applications and re-establishment of biological equilibrium neither of those dampers is especially effective.  Such fluctuations, while frightening and frustrating, should be seen not as signs of failure, but of progress.  While dealing with such swings may be challenging, dealing with the perceptions of other farmers and the larger rural community may be even more difficult. As one farmer wryly observed during this phase of the shift, "Right now, the worst weed problem I've got is down at the coffee shop."

Although the health and environmental difficulties associated with conventional pesticides justify a significant change of approach, a great deal of improvement can be made with relatively little risk.  Sustainable production goes far beyond simply reducing the quantities of chemicals applied.  It involves numerous positive steps, many of which can be initiated without having to make major shifts in pest management strategies at the very beginning.

Weed management is one of the most challenging activities in low-chemical and sustainable production systems.  A basic understanding of weed ecology and the influence of cropping patterns on weed communities will help growers refine their use of cultural and mechanical techniques, thereby reducing the time required for effective weed control.

Because herbicides are used sparingly in sustainable production, prevention of weed problems is a fundamental component of management.  In general terms, weed prevention is based on developing a sound rotation, thwarting all attempts by existing weeds to set seed, and by minimizing the arrival of new weed seeds from outside the field.

While a good weed prevention program will decrease weed pressure substantially, successful crop production still requires a well-conceived program for controlling weeds to the point that they have no negative impact on net income.  Weed control programs include a range of carefully timed cultivations and other mechanical interventions designed to kill as many young seedlings as possible.

A well-developed sense of timing is essential for effective weed management.  Delayed seeding, for example, can be  combined with pre-plant tillage to control early-germinating weeds.  The farmer will need to know how long seeding can be delayed without compromising yields; also, when to work the soil to stimulate maximum weed emergence so they can be rapidly and easily killed.  In other instances relatively early seeding may be preferred (if soil temperatures permit) to get a jump on later-emerging weeds.

Unfortunately, the scheduling of weed control operations is often hindered by unfavorable weather conditions.  It may also be complicated by operational timing intended to thwart other crop pests.  ATTRA has additional information on weed control options for both agronomic and horticultural crops, available on request, including a recent publication entitled Principles of Sustainable Weed Management.

Insect pests can have a serious impact on farm income.  In balanced farm production systems, insect pests are always present.  However, massive outbreaks resulting in severe economic damage are minimized.  This results in good part from the presence of natural control agents ¾ especially predatory and parasitic insects, mites and spiders—that keep pest populations in check. Restoring this population of beneficial arthropods is one of the objectives of a well-planned transition.  The two basic features of transition planning to restore populations of beneficials are:
 

1. The cessation or reduction of practices which  destroy beneficials.  Most importantly, this  entails reducing pesticide usage and/or the  careful timing of applications.

 
2. Management of habitat for beneficials in the  form of protected zones, cover crops, com panion plants, etc.  Management of habitat for  beneficials is sometimes called farmscaping.   ATTRA's publication Farmscaping for Biological  Control provides details on theory and  implementation of this concept.

Farmers need to consider carefully how to manage the shift to fewer pesticides during the first few years, before beneficial insect populations have rebuilt to levels where they can exert significant control of the major pests.  Farmers should plan to work closely with local experts — especially farmers with transition experience — to ensure as smooth a shift as possible.

Actually, the first step towards preventing serious insect problems in any cropping system is the production of healthy plants which are, in turn, nurtured by a microbially active soil enriched with organic matter and a balanced mineral diet.  This belief — that a healthy soil produces healthy plants more resistant to insect and disease attack — is a fundamental principle of organic agriculture and has arisen from decades of largely undocumented field observations by practicing farmers.  More recently, however, this viewpoint has become accepted as fact among many soil scientists and others in the scientific community (10).

Sooner or later nearly every grower confronts unacceptable pest pressure, making some method of pest control necessary. Integrated pest management (IPM) is the basic framework used to decide when and how pests are to be controlled.  The primary goal of IPM is to provide clear pest management guidelines to growers in order to optimize pest control in an economically and ecologically sound manner.

IPM integrates habitat modification, cultural, physical, biological, and chemical practices to minimize crop losses.  Monitoring, record keeping, and life cycle information about pests and their natural enemies are used to determine which control options are needed to keep pests below an economically damaging threshold.  IPM also involves specific techniques to manage pests,  summarized in the ATTRA publication Integrated Pest Management.

One class of techniques used in pest management, and already discussed in brief, is biological control.  Biological control is the use of living organisms to control crop pests.  Biocontrol agents may be predatory, parasitic, or pathogenic; they may also be either "natural" (from naturally occurring organisms such as wild beneficial insects) or "applied" (meaning the organisms are introduced).  Biocontrol agents include insects, mites, bacteria, fungi, viruses, and nematodes.  Certain beneficial nematodes (Steinernema sp., for example) transmit pathogens to their prey, and could be seen as a form of indirectly applied biocontrol.

Farms exploring IPM concepts for the first time may limit their involvement to monitoring levels of one or two pests on a secondary crop, applying their usual insecticide if the threshold of economic injury is approached. Others may shift from a broad-spectrum insecticide such as Guthion™ to a more beneficial-friendly material, such as Imidan™.  As operator comfort with IPM increases, it is common to apply basic concepts to the primary crop and expand IPM management on the secondary crop—perhaps through the introduction of beneficial parasites or predators of the target pest insect.

As they move towards greater sustainability, IPM programs tend to go through three phases, with each stage using and building on previous knowledge and techniques (11):
 

1. The pesticide management phase, characterized by establishing economic thresholds, sampling, and spraying as needed.

 
2. The cultural management phase, based on a thorough understanding of the pest's biology and its relationship to the cropping system.  Tactics employed to control pests include delayed planting dates, crop rotation, altering harvest dates, etc.

 
3. The biological control phase, or "bio-intensive IPM," requires thorough understanding of the biology of natural enemies (in addition to that of the pest) and an ability to measure how effective these agents are in controlling pests.  When natural agents do not meet expected goals, "soft" pesticides (relatively non-toxic to nontarget organisms) are used, and applications are timed to minimize pesticide exposure of beneficials.

Because sustainable production depends on such bio-intensive IPM for its long-term success, a working knowledge of the life cycles of pests and their natural enemies is very important.  The aim is to identify and exploit the weak link in a pest's life cycle.  Several good books and publications on insect identification are available through Cooperative Extension; more may be found in local libraries and bookstores.

When all other integrated pest management tactics are unable to maintain insect pest populations below economic thresholds, insecticide application to control the pests and prevent economic loss is clearly justified.  In such cases, sustainable farmers will usually attempt to obtain satisfactory control using one of the "biorational" pesticides.

Biorational pesticides are fairly pest specific and usually non-persistent, causing a minimal amount of harm to beneficial organisms.  Biorational pesticides may include some conventional synthetic pest control materials, but more typically embody the microbial insecticides like Bacillus thuringiensis or Beauveria bassiana; insecticidal soaps; pheromones (for trapping or mating disruption), and insect growth regulators. Botanical plant extracts like neem and ryania are also known as least-toxic, narrow-spectrum controls combining minimal negative impact on beneficial species with very rapid decomposition in the environment.

Disease management through cultural means is considered the most sustainable methodology.  Techniques and strategies include crop rotation, resistant cultivars, good soil drainage, adequate air movement , and planting clean seed.  These may be supplemented through the use of biorational fungicides.  As with insect pest management, integrated management principles should be applied, including monitoring of environmental conditions, to determine whether preventative fungicidal sprays are required.

With the exception of a few plant extracts used in Biodynamic™ farming, fungicides in organic production systems have largely been limited to copper and sulfur-based products.  Most coppers are labeled for anthracnose, early and late blight, gray leaf mold, and Septoria leaf spot. Sulfur is labeled for control of powdery mildew and is also effective as a miticide and mild insecticide.  Coppers also function as bactericides in the control of bacterial diseases such as bacterial spot and bacterial speck.  Several copper formulations are available commercially.  In recent years, some new and interesting disease management materials have been identified.  These include:
 

Compost extracts (also called compost  "teas.")

Fungal antagonists.  Beneficial fungi capable of preventing colonization of the crop by pathogens.

Baking soda.  A least-toxic fungicide  against several diseases and is, apparently,  not harmful to beneficials.

Plant extracts. As commonly used in  Biodynamic™ agriculture.

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Key Ideas For Transition to Sustainable Farming:

As mentioned earlier, it is risky to rely on recipes, but that being said, there is a general transition path that has worked well for many farmers (5,6,7) over the years.
 

1. Lengthen and diversify the rotation from the very beginning of the transition, before making any significant changes in the management of individual crops. Such attention to the rotation is significantly easier under the 1996 Farm Bill than under the restrictions of previous legislation.
   
   
2. CORN - BEANS - OATS - ALFALFA - ALFALFA or CORN - BEANS - OATS - CLOVER are two proven rotations for corn and bean growers (5,6,7), while VEGETABLES - VEGETABLES - VEGETABLES - CEREAL - CLOVER - CLOVER is popular with conscientious vegetable growers (6,7)
   
   
3. In stone-free soils, use the rotary hoe enthusiastically in corn and bean crops, while reducing herbicide dosage rates.  Delayed planting may allow for extra pre-plant mechanical weed control as long as cutworms don't become problematical.
   
   
4. If at all possible, eliminate anhydrous ammonia from the fertility program because it is so damaging to soil life.  Reduce all chemical nitrogen applications by 25% from the outset, and by another 25% once the rotation cycle is well-established.  Shift to a sulfate of potash-magnesia and mono-ammonium phosphate based blend of starter fertilizer.  Work to discontinue all chemical nitrogen, replacing it with legume plowdown crops and composted manure.
   
   
5. If manure is applied, begin to use a more aerobic handling system. Consider composting; the ATTRA publication Farm-Scale Composting contains much useful material.
   
   
6. Get involved with a local organic farmers group—the members are a wealth of practical, region-specific information.
   
   
7. Learn about Holistic Management  or another means of sound, holistic decision-making and apply the principles to the farming operation.  Consider working with an experienced consultant to identify trouble spots and to develop a more detailed plan for transition.
   
   
8. Get to know the major pests, their life cycles, and the beneficials that attack them. Make the farm more attractive to those beneficials.  Develop primary, secondary, and alternate pest management plans for all major pests of the crops grown.
   
   
9. Continue to replace herbicides with mechanical weed control; pay special attention to the timing of weed control activities—it's more important than the specific equipment used.
   
   
10. Remember that transition will take time and the approaches used in the beginning may no longer be appropriate as the system changes and improves.
    
    

A FINAL NOTE

It is important to remember that each farm system is unique.  The needs, goals, and abilities of each farm family are distinct; the strengths and weaknesses of each farm unit are different.  Nevertheless, the skills, abilities, and knowledge acquired in the course of shifting from a product-focused approach towards a more management-based strategy of collaboration with nature offer many rewards—financial, personal, and ecological.

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References:
 

1. Horne, James E. and Ken Williams.  1993.  Farming Systems Criteria: Ten Principles of  Sustainability.  The Kerr Center for Sustainable Agriculture, Poteau, OK.  2 p.
        Available free of charge from:
               The Kerr Center for Sustainable Agriculture
               P.O. Box 588
               Poteau, OK  74953
               918-647-9123
   
   
2. Center for Holistic Management
   1010 Tijeras, M.W.
   Albuquerque, New Mexico, 87102
   505-842-5252
   
   
3. Petrzelka, Peggy.  1995.  Crop Consulting in Iowa.  Iowa State University, Ames, Iowa.  4 p.
   
   
4. Hudson, Berman D.  1994.  Soil organic matter  and  available water capacity.  J. Soil and Water Cons.   Vol. 49, p. 189–94.
   
   
5. Kansas Rural Center
   PO Box 133
   Whiting, Kansas, 66552-0133
   913-873-3431
   
   
6. Organic Crop Improvement Association
   1001  Y  Street, Suite B
   Lincoln, Nebraska, 68508-1172
   402-477-2323
   
   
7. Martin, Wayne et. al.  1991-95.  Numerous farmers' personal communication during organic  certification inspections in Kansas, Iowa, Wisconsin, Minnesota, Missouri, Pennsylvania,  Illinois, Indiana, North Dakota, Nebraska, and  Alberta.
   
   
8. Abdul-Baki, Aref A. and John R. Teasdale.  1994.   Hairy vetch cover crop provides all the N  required by tomato crop (abs.).  American Society of  Horticultural Science Annual Meeting, Oregon  State University, Corvallis.
   
   
9. Parnes, Robert.  1990.  Fertile Soil.  agAccess,  Davis, California.  p. 51-58.
   
   
10. Ingham, Elaine.  1997.  The Soil Foodweb: It's  Importance in Ecosystem Health.
          http://rain.org:80/~sals/ingham.html
    
    
11. Ferro, D.N.  1993.  Integrated pest management in  vegetables in Massachusetts.  p. 95–105.  In:  Anne  R. Leslie, and Gerrit W. Cuperus (ed.)  Successful Implementation of Integrated Pest Management  for Agricultural Crops.  Lewis, Boca Raton, Florida.

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Prepared by Bart Hall & George Kuepper
ATTRA Technical Specialists
December 1997
http://www.attra.org/attra-pub/trans.html