LEGUME COVER CROP CONTRIBUTIONS TO NO-TILLAGE CORN PRODUCTION

Winter cover crops can supply N to the next crop, reduce erosion and N leaching, and conserve or deplete soil moisture. To identify optimum corn fertilizer nitrogen (FN) rates following cover crops, we evaluate d hairy vetch (VT: Vicia villosa Roth), Austrian winter pea [PE: Pisum sativum L. subsp. sativum var. arvense (L.) Poir.], crimson clover (C R: Trifolium incarnatum L.), and wheat (WH: Triticum aestivum L.) wint er cover crops in the U.S. Coastal Plain and Piedmont, for no-tillage corn (Zea mays L.) at four FN rates (topdressed NH4NO3) over 4 yr. Par ameters evaluated included cover crop yield and N content, corn N upta ke, and corn grain yield. On the Coastal Plain, VT, PE, CR, and WH top growth averaged 205, 180, 170, and 40 kg N ha-1, respectively, and alm ost-equal-to 40% less for the Piedmont. With no FN, grain yields were generally greater after legumes than after no cover crop, and lowest a fter WH, with the best yields after legumes with 90 to 135 kg FN ha-. Synergistic responses occurred when FN was applied after legumes. Non- N-limited grain yield increases averaged 2 Mg ha-1 (Coastal Plain) and 0.5 Mg ha-1 (Piedmont), and were not directly related to cover crop N . With no cover crop, FN needed for maximum yield averaged 80 kg ha-1 (Piedmont) and 135 kg ha-1 (Coastal Plain). After WH, FN needs increas ed 15 to 30 kg ha-1, but decreased 10 to 75 kg ha-1 after legumes. Hai ry vetch provided the most consistent increases, with average grain yi eld of 10.6 Mg ha-1 (Coastal Plain) and 8.2 Mg ha-1 (Piedmont), and an economic optimum FN rate of 127 (Coastal Plain) and 66 kg ha-1 (Piedm ont).