Corn Yield Response to Pre-Plant N Rates Following Cover Crops.

Winter wheat is grown in many poorly drained soils in the northern areas of the eastern Corn Belt to diversify crop and field management, but the fields are often left fallow. Cover crops could be planted in these fields to conserve soil, to reduce weed pressures, and to scavenge nutrients (e.g., nitrogen) for the following corn crop. Our objective was to determine the nitrogen requirement for the subsequent corn crop as affected by cover crop management system. Field studies were conducted in Northeastern Indiana under the following field management sequence: winter wheat (fall, winter, summer), manure application after wheat harvest (summer), cover crops planted late summer and terminated the following spring, and corn season. Therefore, the first field management system started Fall 2012 (i.e., winter wheat planting) and ended Fall 2014 (i.e., corn harvest) and the second field management system started in Fall 2013 and ended Fall 2015. Half of the study received swine manure in a randomized complete block design. The 12 cover crop treatments following wheat harvest were fallow, double crop soybean (not for grain), oats, oats + oilseed radish, cereal rye (CR), CR + oilseed radish, CR + crimson clover, CR + oats + oilseed radish + crimson clover (CR mix), annual ryegrass (AR), AR + oilseed radish, AR + crimson clover, and AR + oats + oilseed radish + crimson clover (AR mix). Following cover crop termination, five rates of pre-plant UAN (28% N) was applied at 67.3 kg N ha^-1 increments from 0 to 269 kg N ha^-1. All corn plots were planted with an additional 33.6 kg N ha^-1 in a starter band. Highest maximum corn yields (11.7 Mg ha^-1 without manure, and 12.5 Mg ha^-1 with manure application) and lowest agronomic optimum N rates were achieved under the fallow, double crop soybean (not for grain), oats, and AR mix systems. Lowest maximum corn yields (10.4 Mg ha^-1 without manure, and 11.5 Mg ha^-1 with manure application) and highest agronomic optimum N rates were observed following cereal rye alone and annual ryegrass alone. Improvements in corn yield were observed as oilseed radish, crimson clover or the full mix was added to annual ryegrass with minimal improvements as these were added to cereal rye.