Application effects of coated urea and urease and nitrification inhibitors on ammonia and greenhouse gas emissions from a subtropical cotton field of the Mississippi delta region.

Abstract Nitrogen (N) fertilization affects both ammonia (NH 3 ) and greenhouse gas (GHG) emissions that have implications in air quality and global warming potential. Different cropping systems practice varying N fertilizations. The aim of this study was to investigate the effects of applications of polymer-coated urea and urea treated with N process inhibitors: NBPT [N-(n-butyl)thiophosphoric triamide], urease inhibitor, and DCD [Dicyandiamide], nitrification inhibitor, on NH 3 and GHG emissions from a cotton production system in the Mississippi delta region. A two-year field experiment consisting of five treatments including the Check (unfertilized), urea, polymer-coated urea (ESN), urea + NBPT, and urea + DCD was conducted over 2013 and 2014 in a Cancienne loam (Fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). Ammonia and GHG samples were collected using active and passive chamber methods, respectively, and characterized. The results showed that the N loss to the atmosphere following urea-N application was dominated by a significantly higher emission of N 2 O-N than NH 3 -N and the most N 2 O-N and NH 3 -N emissions were during the first 30–50 days. Among different N treatments compared to regular urea, NBPT was the most effective in reducing NH 3 -N volatilization (by 58–63%), whereas DCD the most significant in mitigating N 2 O-N emissions (by 75%). Polymer-coated urea (ESN) and NBPT also significantly reduced N 2 O-N losses (both by 52%) over urea. The emission factors (EFs) for urea, ESN, urea-NBPT, urea + DCD were 1.9%, 1.0%, 0.2%, 0.8% for NH 3 -N, and 8.3%, 3.4%, 3.9%, 1.0% for N 2 O-N, respectively. There were no significant effects of different N treatments on CO 2 -C and CH 4 -C fluxes. Overall both of these N stabilizers and polymer-coated urea could be used as a mitigation strategy for reducing N 2 O emission while urease inhibitor NBPT for reducing NH 3 emission in the subtropical cotton production system of the Mississippi delta region.