Corn Yield and NUE with Nitrogen Application at Early Vegetative and Reproductive Stage.

Split application of N fertilizer is a topic that is receiving considerable attention. Previous research in Kansas has shown that split N applications can increase yield compared to all pre-plant N fertilizer applications. This study was designed to evaluate current N fertilizer recommendations for a split N application system with emphasis on late-vegetative and early-reproductive N application times. Four corn studies were established in North Central and Eastern Kansas. Sites were no-tilled into soybean residue including irrigated and dryland. The studies were fertilized with urea-ammonium nitrate (UAN) at two corn growth stages (V4 and R1). Ten N rates were applied, based on the Kansas State Univ. recommendations with rates that varied from the recommendation by -56, -28, 0, +28, and +56 kg N/ha were applied. Approximately 60% of the N was applied at V4 and the reminding 40% at R1. We collected SPAD meter readings before and after the second N application, collected ear leaves at R1-R2 and whole plants at R5.5, and yield. We observed yield differences between 0 N controls and fertilizer treatments at three sites, while the forth site did not have statistically significant differences. There were no differences in yield between rates, but some statistically significant differences in NUE and N uptake depending on the site. These results suggest that current N recommendations may require adjustments when N fertilizer applications are split-applied for high yielding corn.