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Home  > Question of the Week

Question of the Week

Permalink What are the benefits of cover crops?

Answer: Cover crops could be considered the backbone of any annual cropping system that seeks to be sustainable. There are several ways to use cover crops, each delivering specific benefits for your crops or soil.

A cover crop is any crop grown to provide soil cover, regardless of whether it is later incorporated. Cover crops are grown primarily to prevent soil erosion by wind and water. "Green manuring" involves the soil incorporation of any field or forage crop while green or soon after flowering, for the purpose of soil improvement.

Cover crops and green manures can be annual, biennial, or perennial herbaceous plants grown in a pure or mixed stand during all or part of the year. In addition to providing ground cover and, in the case of a legume, fixing nitrogen, they also help suppress weeds and reduce insect pests and diseases. When cover crops are planted to reduce nutrient leaching following a main crop, they are often termed "catch crops."

A living mulch is a cover crop that is interplanted with an annual or perennial cash crop. Living mulches suppress weeds, reduce soil erosion, enhance soil fertility, and improve water infiltration. Examples of living mulches in annual cropping systems include overseeding hairy vetch into corn at the last cultivation, no-till planting of vegetables into subclover, sweetclover drilled into small grains, and annual ryegrass broadcast into vegetables. Living mulches in perennial cropping systems are simply the grasses or legumes planted in the alleyways between rows in orchards, vineyards, Christmas trees, berries, windbreaks, and field nursery trees to control erosion and provide traction.

The benefits of cover crops and green manures are listed below.

Organic Matter and Soil Structure
A major benefit obtained from green manures is the addition of organic matter to the soil. During the breakdown of organic matter by microorganisms, compounds are formed that are resistant to decomposition—such as gums, waxes, and resins. These compounds—and the mycelia, mucus, and slime produced by the microorganisms—help bind together soil particles as granules, or aggregates. A well-aggregated soil tills easily, is well aerated, and has a high water infiltration rate. Increased levels of organic matter also influence soil humus. Humus—the substance that results as the end product of the decay of plant and animal materials in the soil—provides a wide range of benefits to crop production.

Nitrogen Production
Nitrogen production from legumes is a key benefit of growing cover crops and green manures. Nitrogen accumulations by leguminous cover crops range from 40 to 200 pounds of nitrogen per acre. The amount of nitrogen available from 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 encourage good nitrogen production include getting a good stand, optimum soil nutrient levels and soil pH, good nodulation, and adequate soil moisture.

Soil Microbial Activity
A rapid increase in soil microorganisms occurs after a young, relatively lush green manure crop is incorporated into the soil. The soil microbes multiply to attack the freshly incorporated plant material. During microbial breakdown, nutrients held within the plant tissues are released and made available to the following crop. Factors that influence the ability of microorganisms to break down organic matter include soil temperature, soil moisture, and carbon-to-nitrogen (C:N) ratio of the plant material.

Nutrient Enhancement
In addition to nitrogen from legumes, cover crops help recycle other nutrients on the farm. Nitrogen (N), phosphorous (P), potassium (KB), calcium (Ca), magnesium (Mg), sulfur (S), and other nutrients are accumulated by cover crops during a growing season. When the green manure is incorporated, or laid down as no-till mulch, these plant-essential nutrients become slowly available during decomposition. Dr. Greg Hoyt developed a method for estimating nutrient accruement by cover crops in order to reduce the soil test recommendation of fertilizer for the following crop.

Rooting Action
The extensive root systems of some cover crops are highly effective in loosening and aerating the soil. In Australian wheat experiments, the taproots of a blue lupine cover crop performed like a "biological plow" in penetrating compacted soils. When cover crops are planted after a subsoiling treatment, they help extend the soil-loosening effects of the deep tillage treatment.

Weed Suppression
Weeds flourish on bare soil. Cover crops take up space and light, thereby shading the soil and reducing the opportunity for weeds to establish themselves. The soil-loosening effect of deep-rooting green manures also reduces weed populations that thrive in compacted soils.

The primary purpose of a non-legume green manure—such as rye, millet, or sudangrass—is to provide weed control, add organic matter, and improve soil tilth. They do not produce nitrogen. Thus, whenever possible, annual grain or vegetable crops should follow a legume green manure to derive the benefit of farm-produced nitrogen.

Soil and Water Conservation
The soil conservation benefits provided by a cover crop extend beyond protection of bare soil during non-crop periods. The mulch that results from a chemically or mechanically killed cover crop in no-till plantings increases water infiltration and reduces water evaporation from the soil surface. Soil cover reduces soil crusting and subsequent surface water runoff during rainy periods.

Pest Management Benefits of Cover Crops
In addition to the soil-improving benefits, cover crops can also enhance many pest-management programs. Ecologists tell us that stable natural systems are typically diverse, containing many different types of plants, arthropods, mammals, birds, and microorganisms. Growing cover crops adds diversity to a cropping system. In stable systems, serious pest outbreaks are rare because natural controls exist to automatically bring populations back into balance.

Farmers and researchers in several locations have observed and documented increased beneficial insect numbers associated with cover crops. The cover crops provide pollen, nectar, and a physical location for beneficial insects to live while they search for pest insects.

Conservation tillage proves a better option than tilling because it leaves more crop residue on the surface to harbor the beneficial insects. Strip tilling or no-tillage disturbs a minimum of the existing cover crop that harbors beneficial insects. Cover crops left on the surface may be living or in the process of dying. At either of these stages, they protect beneficials. Once the main crop is growing, the beneficials move onto it. By having the cover crop in place early in the growing season, the population of beneficials is much higher sooner in the growing season than would be the case if only the main crop were serving as habitat for the beneficials.

For more information on cover crops and green manures, see ATTRA publication Overview of Cover Crops and Green Manures at This publication summarizes the principal uses and benefits of cover crops and green manures. Brief descriptions and examples are provided for winter cover crops, summer green manures, living mulches, catch crops, and some forage crops. To impart a sense for the importance of these practices in sustainable farming, the publication summarizes the effect of cover crops and green manures on organic matter and soil structure, nitrogen production, soil microbial activity, nutrient enhancement, rooting action, weed suppression, and soil and water conservation. Management issues addressed include vegetation management, limitations of cover crops, use in crop rotations, use in pest management, and economics of cover crops. A selection of print and Web resources are provided for further reading.

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Permalink How do I develop and maintain productive and profitable soil?

Answer: The soil, the environment, and farm condition benefit when the soil's natural productivity is managed in a sustainable way. Reliance on purchased inputs declines year by year, while land value and income potential increase. Some of the things we spend money on can be done by the natural process itself for little or nothing. Good soil management produces crops and animals that are healthier, less susceptible to disease, and more productive.

Any farmer will tell you that good soil:
• feels soft and crumbles easily
• drains well and warms up quickly in the spring
• does not crust after planting
• soaks up heavy rains with little runoff
• stores moisture for drought periods
• has few clods and no hardpan
• resists erosion and nutrient loss
• supports high populations of soil organisms
• has a rich, earthy smell
• does not require increasing inputs for high yields
• produces healthy, high-quality crops

All these criteria indicate a soil that functions effectively today and will continue to produce crops long into the future. These characteristics can be created through management practices that optimize the processes found in native soils.

Soils are made up of four basic components: minerals, air, water, and organic matter. In most soils, minerals represent around 45% of the total volume, water and air about 25% each, and organic matter from 2% to 5%. The mineral portion consists of three distinct particle sizes classified as sand, silt, or clay. Sand is the largest particle that can be considered soil.

An acre of living topsoil contains approximately 900 pounds of earthworms, 2,400 pounds of fungi, 1,500 pounds of bacteria, 133 pounds of protozoa, 890 pounds of arthropods and algae, and even small mammals in some cases. Therefore, the soil can be viewed as a living community rather than an inert body. Soil organic matter also contains dead organisms, plant matter, and other organic materials in various phases of decomposition. Humus, the dark-colored organic material in the final stages of decomposition, is relatively stable. Both organic matter and humus serve as reservoirs of plant nutrients; they also help to build soil structure and provide other benefits.

The type of healthy living soil required to support humans now and far into the future will be balanced in nutrients and high in humus, with a broad diversity of soil organisms. It will produce healthy plants with minimal weed, disease, and insect pressure. To accomplish this, we need to work with the natural processes and optimize their functions to sustain our farms.

Considering the natural landscape, you might wonder how native prairies and forests function in the absence of tillage and fertilizers. These soils are tilled by soil organisms, not by machinery. They are fertilized too, but the fertility is used again and again and never leaves the site. Native soils are covered with a layer of plant litter and/or growing plants throughout the year. Beneath the surface litter, a rich complexity of soil organisms decompose plant residue and dead roots, then release their stored nutrients slowly over time. In fact, topsoil is the most biologically diverse part of the earth. Soil-dwelling organisms release bound-up minerals, converting them into plant-available forms that are then taken up by the plants growing on the site. The organisms recycle nutrients again and again with the death and decay of each new generation of plants.

Soil management involves stewardship of the soil organisms. The primary factors affecting organic matter content, build-up, and decomposition rate in soils are oxygen content, nitrogen content, moisture content, temperature, and the addition and removal of organic materials. All these factors work together all the time. Any one can limit the others. These are the factors that affect the health and reproductive rate of organic matter decomposer organisms. Managers need to be aware of these factors when making decisions about their soils. Let's take them one at a time.

Increasing oxygen speeds decomposition of organic matter. Tillage is the primary way extra oxygen enters the soil. Texture also plays a role, with sandy soils having more aeration than heavy clay soils. Nitrogen content is influenced by fertilizer additions. Excess nitrogen, without the addition of carbon, speeds the decomposition of organic matter. Moisture content affects decomposition rates. Soil microbial populations are most active over cycles of wetting and drying. Their populations increase following wetting, as the soil dries out. After the soil becomes dry, their activity diminishes. Just like humans, soil organisms are profoundly affected by temperature. Their activity is highest within a band of optimum temperature, above and below which their activity is diminished.

Adding organic matter provides more food for microbes. Organic matter must be renewed from plants growing on the soil, or from animal manure, compost, or other materials imported from off site. When soil organisms are fed, fertility is built up in the soil, and the soil will feed the plants. To achieve an increase of soil organic matter, additions must be higher than removals. The formation of new humus is essential to maintaining old humus, and the decomposition of raw organic matter has many benefits of its own. Increased aeration caused by tillage coupled with the absence of organic carbon in fertilizer materials has caused more than a 50% decline in native humus levels on many U.S. farms.

Appropriate mineral nutrition needs to be present for soil organisms and plants to prosper. Adequate levels of calcium, magnesium, potassium, phosphorus, sodium, and the trace elements should be present, but not in excess. The base saturation theory of soil management helps guide decision-making toward achieving optimum levels of these nutrients in the soil. Several books have been written on balancing soil mineral levels, and several consulting firms provide soil analysis and fertility recommendation services based on this theory.

Commercial fertilizers have their place in sustainable agriculture. Some appear harmless to soil organisms and provide nutrients at times of high nutrient demand from crops. Anhydrous ammonia and potassium chloride cause problems, however. As noted above, anhydrous ammonia kills soil organisms in the injection zone. Bacteria and actinomycetes recover within a few weeks, but fungi take longer. The increase in bacteria, fed by highly available nitrogen from the anhydrous ammonia, speeds the decomposition of organic matter. Potassium chloride has a high salt index, and some plants and soil organisms are sensitive to chloride.

Tillage can be beneficial or harmful to a biologically active soil, depending on what type of tillage is used and when it is done. Tillage affects both erosion rates and soil organic matter decomposition rates. Tillage can reduce the organic matter level in croplands below 1%, rendering them biologically dead. Clean tillage involving moldboard plowing and disking breaks down soil aggregates and leaves the soil prone to erosion from wind and water. The moldboard plow can bury crop residue and topsoil to a depth of 14 inches. At this depth, the oxygen level in the soil is so low that decomposition cannot proceed adequately. Surface-dwelling decomposer organisms suddenly find themselves suffocated and soon die. Crop residues that were originally on the surface but now have been turned under will putrefy in the oxygen-deprived zone. This rotting activity may give a putrid smell to the soil. Furthermore, the top few inches of the field are now often covered with subsoil having very little organic matter content and, therefore, limited ability to support productive crop growth.

Both no-till and reduced-tillage systems provide benefits to the soil. The advantages of a no-till system include superior soil conservation, moisture conservation, reduced water runoff, long-term buildup of organic matter, and increased water infiltration. A soil managed without tillage relies on soil organisms to take over the job of plant residue incorporation formerly done by tillage. On the down side, no-till can foster a reliance on herbicides to control weeds and can lead to soil compaction from the traffic of heavy equipment.

Pioneering development work on chemical-free, no-till farming is proceeding at several research stations and farms in the eastern United States. As one example, Pennsylvania farmer Steve Groff has been farming no-till with minimal or no herbicides for several years. Groff grows cover crops extensively in his fields, rolling them down in the spring using a 10-foot rolling stalk chopper. This rolling chopper kills the rye or vetch cover crop and creates a nice no-till mulch into which he plants a variety of vegetable and grain crops. After several years of no-till production, his soils are mellow and easy to plant into. Groff farms 175 acres of vegetables, alfalfa, and grain crops on his Cedar Meadow Farm.

Other conservation tillage systems include ridge tillage, minimum tillage, zone tillage, and reduced tillage, each possessing some of the advantages of both conventional till and no-till. These systems represent intermediate tillage systems, allowing more flexibility than either a no-till or conventional till system might. They are more beneficial to soil organisms than a conventional clean-tillage system of moldboard plowing and disking.

Topsoil is the farmer's capital. Sustaining agriculture means sustaining the soil. Maintaining ground cover in the form of cover crops, mulch, or crop residue for as much of the annual season as possible achieves the goal of sustaining the soil resource. Any time the soil is tilled and left bare, it is susceptible to erosion. Even small amounts of soil erosion are harmful over time. It is not easy to see the effects of erosion over a human lifetime; therefore, erosion may go unnoticed. Tillage for production of annual crops has created most of the erosion associated with agriculture. Perennial grain crops not requiring tillage provide a promising alternative for drastically improving the sustainability of future grain production.

For more information on creating healthier soil see ATTRA publication, Sustainable Soil Management at This publication covers basic soil properties and management steps toward building and maintaining healthy soils. Part I deals with basic soil principles and provides an understanding of living soils and how they work. In this section you will find answers to why soil organisms and organic matter are important. Part II covers management steps to build soil quality on your farm. The last section looks at farmers who have successfully built up their soil. The publication concludes with a large resource section of other available information.

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Permalink How can I grow apples organically?

Answer: Apples, Malus sp., are among the most difficult crops to grow organically. They are prone to attack by more pests than perhaps any other crop. Without effective management, the worst of these pests can be devastating—to the fruit, to the grower's spirit, and to the bottom line. To minimize or eliminate chemical inputs while keeping yields and profits sound, the grower must develop a detailed understanding of the orchard as a managed ecosystem. In this regard, there is no substitute for direct observation and experience, along with a willingness to experiment.

Geographic and climatic considerations, cultivar selection, the local pest complex, market prices, production costs, and other factors all influence the design and viability of an organic system. What begins as a fragmented pest-by-pest set of tactics must gradually form an overall management plan in which the various strategies work together as much as possible. The publications Twenty Years of Apple Production Under an Ecological Approach to Pest Management, by Ron Prokopy, and The Apple Grower: A Guide for the Organic Orchardist, by Michael Phillips, are excellent guides for an orchardist transitioning to organic production.

Often, the least-toxic organic approach to pest control is very pest-specific. This is good for the overall health of the ecosystem and for consumers, but it can greatly complicate pest management for crops like apples, which have multiple pests.

The ATTRA publication Apples: Organic Production Guide introduces the major apple insect pests and diseases and the most effective organic management methods. It also includes farmer profiles of working orchards and a section dealing with economic and marketing considerations. There is an extensive list of resources for information and supplies and an appendix on disease-resistant apple varieties. For more information, see the guide at

Additionally, information on organic weed control and fertility management in orchards is presented in a separate ATTRA publication Tree Fruits: Organic Production Overview, available at

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Permalink How can I save energy on my farm?

Answer: There are several ways to save energy on your farm depending on what type of infrastructure and operation you have. The first step to reducing farm energy costs is determining where you use energy in your operation. One way to gauge energy use is to have an accredited agency perform an energy audit on your farm. Several organizations provide farm energy audits, which examine existing energy consumption and determine opportunities for savings through energy efficiency improvements and equipment upgrades. Farm energy calculators are another set of tools to estimate energy consumption and calculate the cost of various energy inputs on your farm.

Energy-efficient lighting options present farmers with new opportunities to reduce electricity costs and help manage farms sustainably. Cost-effective, energy-efficient lighting can be used to improve productivity and safety, and reduce operating costs.

See the ATTRA publication Energy-Efficient Lighting for the Farm, at This publication will introduce you to energy-efficient lighting technologies, and terms used by the lighting industry, and help you select options that meet your farm's lighting requirements.

In today's climate of continually escalating fuel prices, farms must find ways to conserve fuel in order to reduce costs. There are many free or low-cost measures that can provide immediate fuel savings. Some energy-saving measures have an associated cost but offer a cost-effective payback.

See the ATTRA publication, Conserving Fuel on the Farm, at This publication provides useful tips to help you start saving fuel on your farm today. This publication focuses on energy conservation in three areas: fuel storage, vehicle operation and maintenance, and field practices.

Efficient Buildings
Efficient buildings can save money and improve comfort while reducing resource consumption. Designers and builders nationwide are creating new buildings that save energy and water, use fewer material resources, and create less waste. Farmers and ranchers can join in the savings by incorporating efficiency in their plans for new buildings or renovations. Whether you are planning housing, barns, equipment sheds, greenhouses, storage spaces, or even specialized facilities for agritourism or product processing, efficiency is an important consideration.

See the ATTRA publication Energy Efficient Buildings: An Overview at This publication discusses several ways to improve the efficiency of agricultural buildings and provides further references for implementing those strategies. Topics covered include suiting a building to its site, using natural systems, using renewable energy, conserving energy, and conserving material resources in construction.

Especially in times of high energy costs, efficient irrigation equipment is essential to the viability of farms and ranches. Most irrigation systems are not as efficient as they could be. Properly sized, adjusted, and maintained irrigation systems can use a lot less energy. And increasing pump and motor efficiency will save additional energy.

See the ATTRA publication Energy Saving Tips for Irrigators at This publication describes ways that irrigators can save energy to reduce irrigation costs. It describes recommended irrigation system installations, explains how utilities charge their irrigation customers for electricity, and describes common causes of wasted energy, as well as common energy-saving hardware improvements. It also includes a do-it-yourself method to estimate the efficiency of electrically powered irrigation systems.

There are several other ATTRA publications that provide information and tools to save energy on your farm. For a comprehensive list of energy-related ATTRA publications, see

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