Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/21/2006
Publication Date: 2/1/2007
Citation: Clark, A.J., Meisinger, J.J., Decker, M.A., Mulford, R.F. 2007. Effects of a grass-selective herbicide in a vetch-rye cover crop system on corn grain yield and soil moisture. Agronomy Journal. 99:43-48. Interpretive Summary: Management of the cover crop kill date and the species composition of a mixture can affect water use by the covers, moisture conservation of cover crop residues, and grain yield of a subsequent corn crop. Data are needed on cover crop management of hairy vetch - cereal rye mixtures, compared to pure stands, in order to make accurate fertilizer nitrogen recommendations and to optimize moisture conservation by covers. This research was conducted on the Eastern Shore of Maryland and studied corn grain yields and soil moisture in the surface eight inches of soil for the above cover crops as affected by: corn fertilizer nitrogen rates, and the application of a grass selective herbicide to the rye cover in the late March which killed the rye early, but allowed the vetch in the mixture to grow until May. This selective kill of the rye was compared to pure stands of vetch and rye, to a late kill of the vetch-rye mixture, and to a no-cover control. There was no difference in corn fertilizer nitrogen response to late- versus early-kill date of pure rye, or of the vetch-rye mixture. Without a cover crop the two-year average economic optimum fertilizer nitrogen rate was about 135 lb nitrogen per acre. A hairy vetch cover crop replaced about 70 lb nitrogen per acre and the vetch-rye mixture replaced an average of about 12 lb nitrogen per acre. A rye cover crop required an average of 45 lb more nitrogen per acre that the no-cover control. Topsoil moisture beneath growing cover crops was greater than the no-cover control in the spring, and the cover-crop residues provided soil moisture conservation benefits during the summer by reducing evaporation. These results are important to farmers, extension agents, consultants, and soil conservation agents because they show that a vetch-rye cover crop mixture can mitigate the disadvantages of pure rye covers, but the mixture supplies less nitrogen to corn than pure vetch.
Technical Abstract: Cover crop spring kill date and species affect water use by covers, summer moisture conservation, and yield of subsequent corn (Zea mays L.). Data are needed on management of cover-crop mixtures of hairy vetch (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 of the mixtures. A two-year study evaluated a grass-selective herbicide (GSH) applied in late March to a pure rye cover and a vetch-rye mixture, leaving the vetch to accumulate N until early May. These treatments were compared to early-May killed pure rye, pure vetch, a vetch-rye mixture, and a no-cover control. Each cover crop treatment was then subdivided into corn FN-rates of 0, 45, 90, 180 and 270 kg ha -1. Corn grain yields and soil moisture were measured, and showed that yields following pure stands of vetch were ' yields following any other cover crop treatment. 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 required about 50 kg more FN ha-1. Spring soil moisture (0-20 cm) beneath growing covers was ' the no-cover controls throughout the spring and the summer. The results show no significant difference in corn FN response to an early-kill date of rye with a GSH, compared to the conventional late-kill date.