Kill Date of Vetch, Rye, and a Vetch-Rye Mixture: I. Cover Crop and Corn Nitrogen

Spring kill date affects cover crop N content and N availability to subsequent no-till corn (Zea mays L.). This 2-yr study was conducted in 1990 and 1991 at Coastal Plain and Piedmont locations in Maryland to evaluate three cover crop kill dates, three corn planting dates, and four corn fertilizer N (FN) rates following hairy vetch (Vicia villosa Roth), cereal rye (Secale cereale L.) and a vetch-rye mixture. No-cover checks were included for each corn planting date. Fertilizer N rates were 0 to 202 kg ha⁻¹ in the Piedmont and 0 to 270 kg ha⁻¹ for the Coastal Plain. The vetch-rye mixture contained as much or more N than vetch, and more N than rye within each kill date. Cover crop biomass and N content increased for each delay in kill. In a 50-d period from late March until early May, vetch and the vetch-rye mixture accumulated about 2 kg N ha⁻¹ d⁻¹, with total topgrowth N accumulation from 144 to 203 kg ha⁻¹ over two locations and two years. Greatest rye N accumulation was 51 kg ha⁻¹. Corn N content ranged from 37 to 293 kg ha⁻¹, and was significantly affected by FN rate. Within FN rate, N content was greater following vetch or vetch-rye than following rye or no cover, particularly at low FN rates. Corn N content was greater if cover kill and corn planting were delayed until late April or mid-May. This was attributed to greater cover crop N production and mulching effects, and the timing of summer rainfall. Corn FN requirements were greatest following rye or no cover, intermediate following vetch-rye, and least following vetch. This demonstrates that cover crop species and kill date can be managed to conserve N with rye, supply N for the next crop with vetch, or provide both N conservation and N supply with a vetch-rye mixture. Contribution no. 9068 and Scientific Article no. A7747 of the Maryland Agric. Exp. Stn.