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 evaluated hairy vetch (VT: Vicia villosa Roth), Austrian winter pea [PE: Pisum sativum L. subsp. sativum var. arvense (L.) Poir.], crimson clover (CR: Trifolium incarnatum L.), and wheat (WH: Triticum aestivum L.) winter 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. Parameters evaluated included cover crop yield and N content, corn N uptake, and corn grain yield. On the Coastal Plain, VT, PE, CR, and WH topgrowth averaged 205, 180, 170, and 40 kg N ha-1, respectively, and almost-equal-to 40% less for the Piedmont. With no FN, grain yields were generally greater after legumes than after no cover crop, and lowest after 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 increased 15 to 30 kg ha-1, but decreased 10 to 75 kg ha-1 after legumes. Hairy vetch provided the most consistent increases, with average grain yield 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 (Piedmont).