Can Varying Nitrogen Application Rates and Timing Reduce the Environmental Impact of Corn Under Future Climate?.

The high nitrogen (N) requirements of corn often lead to losses as leached nitrate (NO₃^-) and nitrous oxide (N₂O) gas. Adjusting the timing of nitrogen fertilizer application to corn to meet plant demand has been suggested as a means of improving corn N uptake efficiency and reducing N losses, yet results from the literature are equivocal and alternative fertilizing strategies have not been evaluated under changing climate conditions. We simulated corn yield and N losses in Iowa, for 3 N application rates based on the Mean Return to Nitrogen (MRTN) calculator, and 4 N application strategies (single application at planting, single application at V6 growth stage, and two applications split between planting and V6) with the DAYCENT biogeochemical model, using historic (1991-2014) and projected future weather scenarios (2041-2065). The highest N application rate caused significantly higher N₂O and NO₃^- losses for split fertilizer and N additions at planting, compared to MRTN and low N applications. N₂O emissions from 67:33% split applications at high N rates were significantly higher than all other applications. N₂O emissions decreased ~29% for all N treatments under future compared to current climate, but single N fertilization at V6 had the lowest emission increase compared to the other strategies. There was no effect of fertilizer timing on NO₃^- leaching, but NO₃^- leaching increased ~42% under future climate compared to current climate across N timing treatments. Model-based projections suggest that split N applications have significantly less impact on N losses than does the total amount of N fertilizer applied. Thus, under future climate, total N application rate and shifts in timing of precipitation will likely be the important drivers of N loss from corn systems, with lower N₂O emissions at the expense of greater NO₃^- leaching.