Effects of in-Season Fertilization Strategies on Nitrogen Use Efficiency and Yield of Irrigated Corn.

Inefficient use of nitrogen (N) in agronomic crop production can lead to water quality concerns and reduced yields for growers. Nitrogen fertilizer left in the soil after harvest is highly mobile and can leach to groundwater or is subject to gaseous loss. Split applications of N can better match N fertilizer applications with corn N uptake needs and improve N use efficiency. The objective of this study was to quantify the effect of N rate, timing, and application method under central pivot and subsurface drip irrigation on corn grain yield and N use efficiency in Delaware. All plots (with exception of the 0 N control) received pre-plant manure (94 kg ha^-1 plant available N) and starter N fertilizer (N rate = 34 kg ha^-1). Additional plots received in-season N fertilizer applications below (185 kg ha^-1), at (240 kg ha^-1), or above (290 kg ha^-1) current Delaware N recommendations for a realistic goal of 16 Mg ha^-1. Grain yield was determined for each treatment using a weigh wagon. Pre-plant soil, post-harvest grain and residue were collected then analyzed for total N to determine N use efficiency by difference and mass balance methods. In 2014, plots receiving in-season applications of N out yielded plots receiving only manure and starter N (17 vs. 15 Mg ha^-1). Timing and rate of N application in-season did not affect yield. Exceptional growing conditions pushed N efficiency values over 100% for most treatments, suggesting mineralization of manure N was adequate to sustain high yields.