Cover crop mixtures versus single species: Water quality and cash crop yield

Cover crops promote environmental health and agricultural production, but most research in the Midwest focuses solely on winter cereal rye (Secale cereal L.) (CR). We evaluated cover crop mixtures compared to single species in terms of cover crop biomass (n = 32 site-years), cash crop yield (n = 32), and subsurface water quality (n = 17) spanning six sites and the mixture species were CR, radish (Raphanus sativus), and rapeseed (Brassica napus). Before corn (Zea mays L.), the single species was oats (Avena sativa) and the mixture species were oats, radish, and hairy vetch (Vicia villosa). Before soybeans, average fall growth of CR in the single species was significantly greater than or similar to the mixture. Fall growth before corn with oats was significantly less than or similar to the oat mixture. Before soybeans/ during soybean growth, both cover crop treatments had significantly lower spring nitrate-nitrogen (NO3-N) concentrations in soil pore water than the control, and single species had lower concentrations than mixtures. Even with mostly winterkill cover crops before corn, spring NO3-N concentrations of soil pore water were significantly lower in the single species treatment than in the no cover treatment. Cover crop treatments had no influence on corn yield overall and slight negative influence on soybean yield at two of the sites. We propose the following to increase diversity of cover crops in the Midwest: CR before soybeans, oats and/ or an oat mixture before corn, and introducing brassicas and hairy vetch in southern Iowa. In this project, these diverse species were possible after broadcast seeding in late August, and that would be our planting recommendation to promote fall growth.