Abstract
In-season N fertilization is increasingly being used as a management strategy to reduce risk of N loss to the environment. This study evaluated the optimal timing for a split N fertilizer application in corn (Zea mays L.) across different environments and soil textural classes in Minnesota. Treatments consisted of pre-plant (PP) urea applied at 0 to 270 or 315 kg N ha(-1) on increments of 45 kg N ha(-1) and five split applications (SA) of 45 kg N ha(-1) urea ammonium nitrate as starter fertilizer and 90 kg N ha(-1) of urea with an urease inhibitor applied at the V2, V4, V6, V8, or V12 stage of corn phenological development. Site-years were grouped according to grain yield response to fertilizer timing. Irrigated coarse-textured soils produced 1.5- to 1.9-fold greater grain yield when fertilizer was split applied from V4 to V12 due to improved synchrony of N availability to crop demand and reduced potential for NO3-N leaching. Rainfed, fine-textured soils had mixed results. Site-years receiving well-distributed precipitation produced greater grain yield when fertilizer was split applied from V2 to V8, but early season N deficiency reduced yield for the V12 application. Site-years with limited precipitation during the late vegetative through grain filling stages of corn had no improvement in grain yield or N use efficiencies for SA because dry soil conditions likely interfered with root development and made N fertilizer positionally unavailable to the crop. This study highlights that the success of SA is largely dictated by soil texture and precipitation.