Soybean Residue Management and Tillage Effects on Corn Yields and Response to Applied Nitrogen

Variability in N fertilizer requirements for corn (Zea mays L.) following soybean [ Glycine max (L.) Merr.] across sites and years emphasizes the need to understand management practice effects on apparent soybean N contributions. This study was conducted to determine the effects of three soybean harvest management systems (HMS) and tillage on subsequent corn grain yields, and apparent soybean N contributions. Field experiments to evaluate the effects of returning or removing soybean residue, soybean forage harvest at the R6 growth stage, and applied N (0–180 kg N ha −1 ) on corn grain yields were conducted for 3 yr at four locations. The soybean residue returned treatment significantly decreased yields by 1.1 and 2.5 Mg ha −1 for 2 of 12 site years. The soybean residue returned treatment also required 134, 41, and 87 kg ha −1 more fertilizer N to maximize yields for 3 of 12 site years, but not at the remaining sites. Greater early season soil NO 3 –N in the forage harvested or residue removed treatments before planting and when corn plants were 30 cm tall (presidedress) is probably a result of warmer soil temperatures and increased soil N mineralization where residue was removed. Economic optimum N rates for corn following soybean varied substantially across sites and years and ranged from 0 to 180 kg N ha −1 but were not greatly affected by soybean HMS or tillage at most sites. This work emphasizes the need for a field‐specific approach to better predict the apparent soybean N contribution to a subsequent corn crop.