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 left in the soil after crop harvest is highly mobile and can leach to groundwater or is subject to gaseous losses. Split additions of N via sidedressing or fertigation can better time N applications with corn N uptake 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 grain yield and N use efficiency in Delaware. The study site was located within the Delaware Inland Bays watershed, in an area of intensive grain crop production that is underlain by a shallow, unconfined aquifer; the aquifer is highly susceptible to contamination. We established irrigated corn on well-drained soil which received pre-plant manure and starter N at 105 and 30 lb/ac, respectively. Center Pivot plots received additional sidedress or fertigation applications below, at, or above current Delaware N recommendations of 0.8, 1.0, and 1.2 lbs/bu expected yield.  Subsurface drip lines applied similar N treatments at rates of 0.8 and 1lb/bu expected yield. Grain yield was determined for each treatment at harvest using a weigh wagon. Pre-plant soil, post-harvest grain and residue, and in-season soil water samples from suction lysimeters were collected and analyzed to determine N use efficiency. Unusually high precipitation confounded results in 2013.  For 2014, we expect highest N use efficiency at rates under current recommendations in fertigated plots.