Managing Irrigated Corn Fertilization with Alternative Nitrogen Sources and Amendments.

A multi-year field study was used to evaluate corn response to nitrogen (N) management strategies at varying N rates and differing N sources under irrigated conditions in the Mississippi Delta in a corn/cotton rotation system.  Three N rates (160, 200, and 240 lb N/acre) and six N source or amendment combinations.  These sources included urea-ammonium nitrate solution (UAN, 32% N), urea (U, 46-0-0), U or UAN plus NutriSphere®, U plus Agrotain®, and ESN (Environmental Smart Nitrogen, polymer-coated urea).  All treatment combinations except ESN were applied as a split application with 100 lb N/acre just after plant emergence and the remainder applied as a sidesress at the V5-V6 growth stage.  All ESN was applied shortly after plant emergence.  The treatments were arranged in a randomized complete block design with four replications and followed cotton in a 1/1 rotation.  All cultural practices were maintained uniformly across the field each year.  Irrigation was supplied through furrow irrigation with approximately 2 inches applied at each irrigation.  The center two rows of each plot were harvested with a sample taken to determine the harvest moisture, bushel test weight, and seed index (100-seed weight).  The liquid fertilizer solution was “knifed-in” to both sides of the row while the dry fertilizer materials were hand-applied, pre-weighed quantities applied to the soil surface and incorporated with cultivation and rainfall.  In 2013, the NutriSphere treatment were eliminated and additional ESN+U or ESN+UAN treatments were included to further evaluate the potential of ESN.  The corn yields have increased with increasing N rates as would be expected with no major differences in the different N sources and amendments.  The urease inhibitors or other products are potentially only effective if weather conditions favor loss.   Depending upon the cost of the inhibitors, they could be effective insurance against possible N loss.