This is the first (hopefully) of series of articles that describe the various Better Management Practices (B.M.P.) promoted by Monacan Soil & Water Conservation District. Editor
by Ken Carter, Associate Director
The use of cover crops in Virginia is at least a century old, but continues to have a vital part in modern agriculture. Basically, cover crops are usually a simple grain, grass, or clover crop planted and grown during the resting period between major cash crops harvested on the land. They provide a variety of benefits to the land and to the farmer’s annual profit. This continues to be true today, and recent agricultural research has shown far more economic and environmental benefits than previously known.
The following is a brief list of the benefits a simple cover crop can provide:
• Erosion control. This is one of the historical uses of cover crops, especially by dairy farmers in the past who, after cutting corn silage to feed their herds, had virtually a bare field. A small grain cover crop was sown in the late summer/early fall and provide a cover to prevent erosion over the winter. Cover crops for erosion control were also used by past generations where fields were idled or left fallow to “rest” for year or more as part of a rotation. Often crops such as clover were added to help enrich the soil. Various planting methods have been used for establishing cover crops such as broadcasting, disking, drilling into the previous crop stubble or other no-till or minimum tillage methods that allow for quick germination and rapid growth.
Cover crops for erosion control is having renewed interest to help control water runoff and surface erosion in low residue modern crops such as soybeans. A cover crop can be planted by broadcasting seed by helicopter or airplane while the crop is still in the field and once the soybeans are harvested the cover crop is already established.
• Nutrient Cycling. As a result of recent agricultural research dealing with nutrients and water quality, it has been found that cover crops can be a major practice to stop the loss of nutrients (primarily nitrogen) into ground and surface water. Planting a small grain cover crop (rye, wheat or other small grain) can take up nitrogen and other soil nutrients from the root zone and prevent them from being lost to ground and surface water. Species such as Abruzzi rye have shown excellent ability to scavenge soil nitrogen and make it available to the next crop grown on the site. Research has shown roots going as far as 5 feet into the subsoil to trap lost nitrogen. Another historic use of cover crop for nutrient cycling is the use of annual clovers such as crimson clover that provides erosion control overwinter yet fixes nitrogen from the air and makes it available for the next year crop. It may not make enough nitrogen available to meet all of the needs of the next crop but can provide measurable amounts. Whenever cover crops are used, soil testing and proper nutrient management should be used to account for the nutrient recycling these cover crops can provide.
• Soil health. In modern agricultural research, soil health has become a new and major area of interest in improving crop yield, nutrient and pest management, and water quality. Cover crops are a major contributor to improving soil quality in the following ways. First, they add organic matter to the soil surface and subsoil layers. Increased organic matter (soil carbon) in the soil profile leads to better aeration, soil tilth*, and improved water movement. Cover crop, as mentioned above, can send roots down 3 to 5 feet. As these roots die, they leave spaces for air and water to reach for down into the soil profile. Secondly, they can help to break up hard pan and traffic pan layers in the soil profile that have develop through years of farm machine compaction. Increased organic matter in the surface leads to better growing conditions for germinating seeds, helps warm the soil in the spring, increases water holding ability, and increases the number of earthworms found in the profile (indicator of healthy soil). Cover crops along with long term no-till cultivation have shown tremendous advantages to soil improvement, crop yields, and reductions of chemical inputs (both fertilizer and pest control chemicals). By developing a strong organic cover on the soil surface (cover crop and crop residue) research and many farmer testimonials have shown lower fertilizer need and much lower amounts of weed killer and insecticide having to be applied. This can lower input costs significantly. It may take a few years to become established, but a healthy soil situation is much more profitable and less input dependent than conventional system.
This can be especially helpful in intensive agricultural crops such as vegetables. Cover crops and green manure crops can return tremendous amount of organic matter back into the soil and aid in water management. This is especially true in organic agriculture were the selection of soil amendments is limited. Species selection in cover crop can also be beneficial to these specialty crops. The use of clovers and/or winter killed oat cover crops can provide erosion control, soil amendments, and soil health improvements without chemical inputs.
• Supplemental grazing. For farms that have cropland agriculture as well as livestock, cover crops can provide benefits to both systems. The crop fields will benefit from all of the items listed above, and the stand of vegetation can be used to provide late spring grazing when hay supplies may be limited or too costly to purchase. Turning cattle into a cover crop can provide days or weeks of early grazing in the spring. Manure from the livestock can also help the fertilizer needs of the next crop.
Cover crops, through many years of use have been and continue to be a major conservation practice that provides multiple benefits to the farm operation and to the basic soil resource.
*Soil tilth: soil suitability for crop growth.
Ken Carter has had a distinguished career in as a State Conservationist with the Natural Resources Conservation Services (N.R.C.S.). Ken Carter now volunteers as an Associate Director for M.S.W.C.D.