Nitrogen Release from Polymer Coated Urea in Five Arkansas Soils.

Environmentally Smart N (ESN, 440 g N kg^-1, Agrium Inc.) is a polymer-coated urea fertilizer being used for the production of row crops. An understanding of the N-release rate of ESN as affected by soil and environmental factors would facilitate development of recommendations.  We evaluated the N-release pattern of ESN incubated in six soils from eastern Arkansas with soil textures ranging from loamy sand to clay.  Six ESN prills (38-44 mg total N) were weighed, placed in mesh bags, and buried in jars that contained 400 g of each soil series (Beulah, Calhoun, Dewitt, Hillemann, Perry, and Sharkey). Soil was incubated at 25ºC and 25% moisture. Bags were unearthed every 5 d after burial (DAB) with a total incubation time of 40 d. The recovered bags were placed in sealed plastic bags and refrigerated until the total-N remaining was determining by combustion. The proportion of initial total N content retained in ESN prills ranged from 0.61 to 0.93 by 10 DAB compared to 0.14 to 0.27 by 40 DAB. The proportion of fertilizer-N remaining in ESN prills declined linearly or nonlinearly across time depending on soil series, with a common intercept term (1.12) shared between all soils.  Linear coefficients were similar among the Beulah (-0.02611x), Hillemann (-0.02148x), and Dewitt (-0.02611x) soils with N release following a straight-line model. Linear and quadratic coefficients were similar among the Calhoun (-0.04535x, 0.00052x²), Sharkey (-0.04713x, 0.00059x²), and Perry (-0.04600x, 0.00057x²) soils with N release proceeding in a curvilinear fashion.  Initial N release proceeded faster in the Calhoun, Sharkey, and Perry soils.  However, by 40 DAB the proportion of ESN-N remaining was statistically similar in all soils.  Results indicate that the N-release rate of ESN differs slightly among soil series.   The reason for the different N release rates is currently unexplained and warrants further research.