Early Vs. Late Nitrogen Strategies for Michigan Corn Production.

Environmental, social, and economic concerns continue to emphasize improving upon current corn (Zea mays L.) nitrogen (N) management strategies. Split-N applications can be used to synchronize N availability with plant N uptake but validation of pre-plant and in-season N strategies is required. Field experiments were conducted from 2014 to 2016 at two locations to investigate three N strategies involving multiple N-placements, timings, and sources applied at a single N rate. Strategies utilized broadcast pre-plant incorporated (PPI) N, starter N applied in-furrow (7.8 kg N ha^-1), or starter N sub-surface banded 5 cm beside and 5 cm below the furrow (44.8 kg N ha^-1). Treatment combinations within the in-furrow and banded starter N strategies included sidedress (SD) at V4-6, V10-12, or 50/50 (split) V4-6 and V10-12. Pre-plant incorporated (PPI) strategies involved 100% urea, 25/75 mix of urea with polymer-coated urea, and poultry litter applied at 2.2 Mg ha^-1 plus SD N V10-12. Canopy V6 NDVI was a significant predictor of final grain yield but variably influenced by N strategy (r² 0.11 to 0.73) and illustrated the importance of meeting early corn N demands. When spring rainfall was at or below normal the in-furrow starter N strategy with delayed SD N application (V10-12) decreased mean grain yield up to 1.4 Mg ha^-1 as compared to other (V4 or split) SD N timings with similar yield trends observed using the sub-surface banded strategy. In wet growing seasons yield potential was maintained using in-furrow or sub-surface banded strategies and delayed SD N application (V10-12) relative to other timings due to avoidance of early-season rainfall. No significant positive yield gains to V10-12 N application suggests use of delayed SD N as a rescue application but not as a standard management practice.