Urease Inhibitors Effect on Ammonia Volatilization and Corn Grain Yield.

One of the main nitrogen (N) loss pathways is ammonia (NH₃) volatilization, which can represent up to 50% of the surface-applied, urea-based fertilizer. Urease inhibitors are chemical compounds designed to inhibit the rate of urea hydrolysis, thus allowing more time for fertilizer to be incorporated into the soil.   Urease inhibitor impacts on NH₃ losses and grain yields have been variable over different environments. Therefore, the objective of this study was to assess how different urease inhibitors impact NH₃ volatilization losses and corn grain yield in two differing environments. Two experiments were conducted, one on a silt loam in 2014 and one on a sandy loam in 2015. Both studies were a randomized complete block design with four replicates. Treatments varied among studies and were comprised of specific combinations among inhibitor type (Agrotain Plus, Agrotain Ultra and LIMUS), N rate (0, 60, 80 and 100% recommended rate) and N timing (preplant x split).  For all fertilizer treatments, urea-ammonium nitrate (UAN) served as the N source with broadcast application. Studies were analyzed independently, with means separation performed using Fisher’s LSD at α=0.05 when a factor was deemed significant.  On the silt loam site in 2014, 80% N and 80% N + Agrotain Ultra had the most NH₃ volatilized at 30d after fertilizer application (19.5 and 19.4 kg N ha^-1, respectively), whereas 80% N + LIMUS lost significantly less (14.7 kg N ha^-1), followed by the 0N control (1.7 kg N ha^-1). Under this same environment, treatments 100% N rate, 80% N + LIMUS and 80% N had the greatest grain yields (12.7,  12.1 and 12.1 Mg ha^-1, respectively), whereas 0N control had the lowest (8.7 Mg ha^-1). On the sandy loam site in 2015, NH₃ volatilization losses were highest under 100% N rate (23.4 kg N ha^-1). Among the fertilized treatments, 80% N + Agrotain Ultra and 80% N + LIMUS had the least NH₃ volatilized (10.4 and 12.4 kg N ha^-1, respectively), with the 0N control having the lowest losses (0.6 kg N ha^-1). Grain yield data for this environment has not been determined by the time of abstract submission and will be included on the oral presentation.  The use of urease inhibitors effectively reduced NH₃ volatilization losses in both environments, although efficacy was higher on the sandy loam site. The effect of urease inhibitors on grain yield was not clear on the silt loam environment. Nonetheless, grain yield impact is expected to be more evident in an environment more prone to N loss such as a sandy loam site.