Tile drainage nitrate losses and corn yield response to fall and spring nitrogen management

Nitrogen (N) management strategies that maintain high crop productivity with reduced water quality impacts are needed for tile-drained landscapes of the US Midwest. The objectives of this study were to determine the effect of N application rate, timing, and fall nitrapyrin addition on tile drainage nitrate losses, corn (Zea mays L.) yield, N recovery efficiency, and postharvest soil nitrate content over 3 yr in a corn-soybean [Glycine max (L.) Merr.] rotation. In addition to an unfertilized control, the following eight N treatments were applied as anhydrous ammonia in a replicated, field-scale experiment with both corn and soybean phases present each year in Illinois: fall and spring applications of 78, 156, and 234 kg N ha^-1, fall application of 156 kg N ha^-1 + nitrapyrin, and sidedress (V5-V6) application of 156 kg N ha^-1. Across the 3-yr study period, increases in flow-weighted NO₃ concentrations were found with increasing N rate for fall and spring N applications, whereas N load results were variable. At the same N rate, spring vs. fall N applications reduced flow-weighted NO₃ concentrations only in the corn-soybean-corn rotation. Fall nitrapyrin and sidedress N treatments did not decrease flowweighted NO₃ concentrations in either rotation compared with fall and spring N applications, respectively, or increase corn yield, crop N uptake, or N recovery efficiency in any year. This study indicates that compared with fall N application, spring and sidedress N applications (for corn-soybean-corn) and sidedress N applications (for soybean-corn-soybean) reduced 3-yr mean flow-weighted NO₃ concentrations while maintaining yields.