Split, Late-Season N Applications Increase Nitrogen Recovery Efficiency in Maize.

In the US Corn Belt, N fertilizer is both a substantial crop input expense and a great environmental concern when lost through leaching or run-off. One solution to ensure more efficient use of N fertilizer in maize is to increase synchrony between crop N demand and soil N availability through split, late-season N applications. This study investigated the agronomic impacts of delaying supplemental, split N applications compared to a single, early sidedress application. A second interest was whether the response in grain yield or N accumulation differed between modern hybrids and hybrids released 20 years ago. In a three-year study comparing N rates ranging from 0-245 kg N ha^-1 either in a single application at V3 or with the last 45 kg N ha^-1 delayed until V12, we found that late-split N applications increased total plant N accumulation and N recovery efficiency. These positive responses were driven by increased post-silking N accumulation (PostN) in the split-N treatments. However, these benefits were not mirrored by any improvement in grain yield. We found little difference in response to the timing of N application in hybrids released in 1991 and 1995 compared to hybrids released in 2012 and 2014. Principle component analysis revealed that PostN had a strong inverse relationship with remobilized vegetative N, while the latter strongly related to R1 N content. Therefore, environments were split-N applications are most likely to realize positive benefits are situations in which corn N accumulation during the vegetative growth stages has been restricted.