Delaware Nutrient Management Notes

COVER CROPS

An important goal of the Delaware Nutrient Management Program is to "...help improve and maintain the quality of Delaware's ground and surface waters..." while working to "...maintain agricultural profitability..." in the State. Agricultural practices that address environmental concerns while offering practical benefits to farmers are a critical part of this process. One such practice is the use of cover crops. These crops not only can reduce the amount of soil loss from wind and water erosion but also can scavenge residual nutrients and release them during the next growing season. This issue will focus on cover crop management in production agriculture.

· A cover crop is any crop planted in a field to provide protection to the soil during a period when row crops are not being grown. This period can be a relatively short time such as a couple of months between spring and fall vegetable crops, or a longer time, such as six months between fall harvest and spring planting.

· During winter, recommended grass species include cereal rye, wheat, and barley although any winter-hardy annual species can be used. Broadleaf species that can be used include winter rape and other leafy Brassica crops. Legume cover crops such as hairy vetch and annual or perennial clovers can be grown to reduce erosion. However, these species are not efficient for scavenging nitrogen from previous crops.

· During summer, grasses such as sudangrass, sorghum-sudangrass hybrids, and others can be effective in protecting soil and trapping nutrients. Non-grasses such as buckwheat also can be effective cover crops.

Benefits of cover crops include:

· Reduced fertilizer bills as nutrients are recycled

· Physical protection of the soil surface which reduces soil loss from wind and water erosion

· Improved water infiltration as soil organic matter increases

· Improvement in soil structure which can enhance soil physical properties and soil water-holding capacity, and can decrease the need for irrigation

· Savings in herbicide costs due to weed suppression associated with long-term cover crop use

· Increased beneficial insect populations associated with certain cover crops

· Reduced soil-borne disease and nematode risks due to active plant growth, and

· Increased capture of residual N applied to previous cash crops, which minimizes the amount of N that can move to groundwater.

· Watersheds in close proximity to sensitive surface waters and/or those most susceptible to ground water contamination by nutrient loss from agricultural fields.

· Soils likely to experience either wind or water erosion that are in close proximity to surface waters.

· Artificially drained soils where shallow ground water discharges rapidly into surface waters.

· Cropping systems that are most likely to have significant amounts of residual nitrate-N in the upper portions of the soil profile in the early fall. Target winter cover crops to previous crops that had below normal yields, in the following order:

a. Dryland corn that received animal manure and/or commercial fertilizer nitrogen.

b. Dryland corn that received only commercial fertilizer.

c. All other corn that received fertilizer or animal manure.

d. Any other crop (e.g. commercial vegetables) that received fertilizer or animal manure.

e. Soybeans that received animal manure, alone or in rotation with a small grain.

f. Soybeans that received no supplemental nitrogen.

g. Grain sorghum.

Winter-hardy grasses with either a deep, dense root system or that produce substantial amounts of aboveground dry matter are excellent choices for recovering residual N. Cereal rye can accumulate up to 60 percent of leftover fertilizer N after a corn crop by mid-April of the next year. Winter wheat also can be used but is less efficient than cereal rye. Although annual ryegrass can recover 53 percent of residual N, this species has the potential to be a severe weed pest in winter wheat grown for grain and caution is required if considering it as a cover crop. Brassica species such as winter rape, Tyfon, turnips, etc., can recover leftover N, up to 75 percent compared with bare fields. To be most effective, Brassica crops must be planted as early as possible and before the end of September. Late planting of any cover crop limits fall growth and nutrient uptake (recovery of leftover N). To maximize cover crop benefit, plant as early as possible, optimize soil-to-seed contact, and plant at the upper end of the suggested seeding rate range. The cover crop should be maintained as late into the spring as practical without running the risk that it will deplete sub- and topsoil moisture levels to the point of being injurious to the next crop.

Prepared by Richard W. Taylor and Dave Hansen, UD Cooperative Extension and the DNMC

Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating. John C. Nye, Dean and Director. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no persons shall be subjected to discrimination on the grounds of race, color, sex, disability, age, or national origin.

Last Updated: Monday, 19-Mar-2007 09:37:30 EDT