Effects of a Grass-Selective Herbicide in a Vetch-Rye Cover Crop System on Corn Grain Yield and Soil Moisture

Cover crop spring kill date and species affect spring water use by covers, summer moisture conservation by cover crop residue, and yield of subsequent corn (Zea mays L.). Data are needed on spring management strategies for cover crop mixtures of hairy vetch (HV) (Vicia villosa Roth) and cereal rye (Secale cereale L.), compared to pure stands, to make accurate corn fertilizer nitrogen (FN) recommendations and to optimize moisture use vs. conservation by cover crop mixtures. A 2-yr study evaluated a grass-selective herbicide (GSH) applied in late March to a pure rye cover and a vetch-rye mixture, allowing the vetch to accumulate N until early May. These treatments were compared to early May-killed pure rye, pure vetch, vetch-rye mixture, and no-cover control. Corn FN rates of 0, 45, 90, 180, and 270 kg ha^-1 were applied in June. Corn grain yield was greater following pure stands of vetch than following any other cover crop treatment, regardless of kill date. The average economic optimum FN rate was about 150 kg N ha^-1 without a cover. With a cover crop and compared to the control, the hairy vetch replaced about 80 kg FN ha^-1, the vetch-rye mixture replaced about 15 kg FN ha^-1, while the pure rye removed an additional 50 kg FN ha^-1. Spring soil moisture (0-20 cm) beneath growing covers was greater than or equal to the no-cover controls throughout the spring and the summer. There was no significant difference in corn FN response for the early kill date of rye with a GSH, compared with the conventional late-kill date.