Managing Cotton Fertilzation with Alternative Nitrogen Sources and Amendments.

Multi-year field studies have been used to evaluate cotton response to nitrogen (N) management strategies at varying N rates and differing N sources under irrigated and rain-fed condition s in the Mississippi Delta.  The studies included three N rates (90 120, and 150 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 60 lb N/acre just after plant emergence and the remainder applied as a sidesress at the pin-head to match-head square growth stage.  All ESN was applied shortly after plant emergence.  The treatments were arranged in a randomized complete block design with four (irrigated) or five (non-irrigated) replications.  All cultural practices were maintained uniformly across each field.  The irrigated study was cotton following corn in rotation while the non-irrigated (rain-fed) study was in a continuous cotton field.  The center two rows of each plot was harvested following defoliation with grab samples taken to determine the lint percentage and lint yields.  Liquid fertilizer solutions were “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.   For the rain-fed study, plots remained in the same location across multiple years.  In 2013, the NutriSphere treatment were eliminated and additional ESN+U or ESN+UAN treatments were included in both studies.  Rain-fed (dryland) lint yields have been more variable than the irrigated yields but neither area has shown much response to N fertilization.  Although ESN is a more expensive N source, a single application of material can save a trip across the field.