Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/1998
Publication Date: N/A
Interpretive Summary: Cover crops provide soil erosion protection, increase soil organic matter, reduce nitrate leaching, and suppress weed growth. In the upper Midwest, however, the potential cover crop growing season between soybean harvest and corn planting is short and cold and allows little growth. This research demonstrates that overseeding oat and rye cover crops into soybean in August rather than after soybean harvest establishes the cover crops before soybean leaf drop and results in more growth in the fall. We showed that overseeding these cover crops usually does not affect soybean yields. Rye, which regrows in the spring, does reduce corn yields when killed with herbicides at corn planting. Oat had no affect on corn yield and because it does not over-winter, it does not produce as much dry matter as rye. Although both oat and rye can be overseeded as cover crops, oat may be more practical because it does not reduce corn yield and does not require herbicides to kill it in the spring. The impact of this research is that it provides producers with a possible management system for small grain cover crops in the upper Midwest. If cover crops were widely adopted in this region, it would improve surface water quality through reduced loading of sediment and nitrate and would improve soil quality and sustainability by increasing soil organic matter and reducing erosion.
Technical Abstract: Cover crops provide soil erosion protection, increase soil organic matter, reduce nitrate leaching, and suppress weed growth. Overseeding small grain cover crops into soybean in August rather than drilling after soybean harvest should provide more time for cover crop growth. The objectives of our study were to measure and compare the dry matter production and surface residue cover produced by oat, rye, and an oat-rye mixture overseeded into soybean in August and to determine the effect of these cover crops on subsequent soybean and corn yield. Oat (1991 to 1996), and rye and an oat-rye mixture (1994 to 1996) were overseeded into soybean at 3 800 000 seeds ha**-1 in field plots near Ames, IA. The oat cover crop significantly reduced soybean yield in only one of six years. The rye and oat-rye mixture treatments did not significantly reduce soybean yield. Corn yields were significantly reduced following rye and oat-rye cover crops, but were not significantly lowered by oat. The rye and oat-rye mixture treatment corn yields averaged 1.6 and 1.3 Mg ha**-1 less than the control. Cover crop shoot dry matter averaged 440 kg ha**-1 in the fall and did not differ among the three cover treatments from 1994 to 1996. Shoot dry matter measured in the spring averaged 1660 kg ha**-1 for the rye and oat-rye mixture and resulted largely from rye growth in the spring. An oat cover crop increased surface residue cover by 7 to 18% from 1991 to 1994. Based on these results, oat overseeded into soybean is a viable cover crop system in the upper Midwest and unlike rye, does not reduce yields of the following corn crop.