Understanding the Microenvironment Surrounding Enhanced Efficiency Urea-Based N-Fertilizer in Soils.

Enhanced efficiency N-fertilizers is one means of increasing nitrogen use efficiency in crop production. Urea, either in granular form or in liquid combination with ammonium nitrate (UAN), is commonly used in the southeast US as well as in other portions of the US as a fertilizer N-source. Commercial formulations that comprise enhanced efficiency N-fertilizers are designed to target specific modes-of-action to slow but not completely inhibit subsequent N-transformations within the soil, in order to increase plant bioavailability and prevent loss from the root zone. Thus, enhanced efficiency N-fertilizers are not intended to impact the bulk soil, but only the immediate soil microenvironment near a given granule or concentrated liquid fertilizer band. This study was designed to elucidate possible modes-of-action whereby a component of Nutrisphere-N^® could inhibit/retard nitrification of ammonium-N derived from treated urea granules when placed in contact with soils. Possible modes-of-action investigated includes metal binding potential of a macromolecule co-polymer, a component of the Nutrisphere-N formulation, in combination with metal bioavailability (Donnan equilibrium dialysis technique) as a function of soil buffer capacity. Metal bioavailability and its impact on microbial derived enzymes is one possible mode-of-action to slow microbial response (e.g. retard nitrification) when a concentrated N-source is introduced into the soil environment. Results from several different soils will be presented from both the southeast and Midwest US.