KILL DATE OF VETCH, RYE, AND A VETCH-RYE MIXTURE .1. COVER CROP AND CORN NITROGEN

Spring kill date affects cover crop N content and N availability to su bsequent 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 e valuate three cover crop kill dates, three corn planting dates, and fo ur corn fertilizer N (FN) rates following hairy vetch (Vicia villosa R oth), 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 O 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 WI date. Cover crop biomass an d N content increased for each delay in Wi. In a 50-d period from late March until early May, vetch and the vetch-rye mixture accumulated ab out 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 accu mulation 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 cont ent was greater following vetch or vetch-rye than following rye or no cover, particularly at low FN rates. Corn N content was greater if cov er kill and corn planting were delayed until late April or mid-May. Th is was attributed to greater cover crop N production and mulching effe cts, and the timing of summer rainfall. Corn FN requirements were grea test following rye or no cover, intermediate following vetch-rye, and least following vetch. This demonstrates that cover crop species and k ill 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 ve tch-rye mixture.