Submitted to: Popular Publication
Publication Type: Popular Publication
Publication Acceptance Date: 1/4/2006
Publication Date: 1/4/2006
Citation: Singer, J.W., Kaspar, T.C. 2006. Cover crop selection and management for midwest farming systems. Iowa Learning Farm Newsletter. Available: http://www.extension.iastate.edu/ilf/.
Technical Abstract: Winter cover crops are planted shortly before or soon after harvest of the cash crop and are killed before or soon after planting of the next cash crop. Cereal grains, such as oat, barley, winter wheat, triticale, and rye are excellent cover crops because they grow rapidly in cool weather, withstand moderate frost, and their seed is relatively inexpensive or can be produced on site. Many varieties of winter rye, triticale, and wheat can overwinter in the upper Midwest and continue growing in the spring. Growth of these winter-hardy cover crops must be terminated with herbicides or tillage prior to planting corn and soybean. Oat, barley, spring wheat and triticale, some rye and winter wheat are not winter-hardy in the upper Midwest. Because the non-winter-hardy cereal grains do not survive the winter, they do not require control prior to planting corn and soybean. Planting small grain cover crops using a no-tillage grain drill or shallow tillage and regular grain drill is recommended. Generally, small grains that overwinter should be planted before Oct. 15 (adjust periods 1 week earlier for northern Iowa and 1 week later for southern Iowa). Small grains that do not overwinter should be planted before mid-September (mid-Iowa) to obtain desirable fall growth. Adapted cultivars of winter rye, wheat, and triticale should be planted at 1 to 1.5 million seeds/acre. Seed size varies considerably from year-to-year and from lot-to-lot. The best way to determine seeding rates on a lb/acre basis is to divide the seeding rate in seeds/acre by seeds/lb. If this information is not available, rough averages to obtain 1.3 million seeds/acre are 90 lb/acre for wheat and triticale (1.5 bu) and rye (1.6 bu). Seeding rates for winter-hardy small grains should also be increased for later planting dates to obtain adequate soil cover for winter erosion protection. Planting rates for oat, barley, and other non-winter-hardy small grains should be increased to 1.5 million seeds/acre, roughly 120 lb/acre of oat (3.75 bu) and 100 lb/acre of barley seed (2.1 bu). Row widths should be 6 to 12 inches with narrower row widths providing better erosion protection. Planting depth should be 0.5 to 1.0 inches. Cover crops can be controlled chemically or mechanically, although mechanical methods vary in their effectiveness. Our experience indicates that it may be beneficial to increase seeding rates for no-tillage corn by 10 percent when preceded by a small grain cover crop. For corn, use a starter (with nitrogen) fertilizer and increase total nitrogen fertilizer rates by 10 percent if less than 150 lb nitrogen/acre. Addition of undecomposed organic matter or crop residues to soil usually results in tie-up or immobilization of nitrogen by the soil microorganisms that are decomposing the organic matter or residues. Eventually, this nitrogen is released back into the soil. Corn yields may be reduced following winter-hardy cereal grain cover crops that are terminated immediately before corn planting. Yield reduction can be minimized by terminating cover crop growth more than 14 days prior to corn planting and using starter fertilizer. Corn yields following an oat cover crop or a legume that overwinters, are not reduced. Soybean yields are not reduced following cereal grain cover crops unless low soil water content limits soybean germination and emergence.