The Nexus of Cover Crops, Water, and Nitrogen: Impact on Corn and Soybean Productivity and the Environment.

The use of cover crops in the corn (Zea mays L.) - soybean [Glycine max (L.) Merr.] rotation is increasing in the Upper Midwest U.S. This temporal and spatial diversification of the system is considered to be positive, but research is needed to advance our understanding on the use of resources like water and nitrogen (N) by cover crops. Field experiments were established across contrasting environments in the Upper Midwest U.S. to study the nexus of cover crops to water and N and its effects on corn and soybean yield and the environment. Winter camelina (Camelina sativa L. Crantz), field pennycress (Thlaspi arvense L.), and winter rye (Secale cereal L.) were used as single winter cover crops. Annual rye [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] and winter rye, each grass mixed with crimson clover (Trifolium incarnatum L.) and forage radish (Raphanus sativus L.), were used as multi-species cover crops. Preliminary results showed differences on water use and environmental benefits between cover crop species and strategy. Cover crops used more water during spring than during fall; this, however, had little to no effect on yield of the primary crops. Nitrate-N in the leachate was higher in the spring than in the fall and varied according to location, cover crop species, and strategy. The effect of cover crops on water and N balances in corn and soybean grown in the Upper Midwest U.S. appear to be marginal during the fall. During the spring, however, cover crops have the potential to affect the water and N balances of the system with beneficial results to corn and soybean production and to the environment.