Nitrogen Fertilizer Source Impacts on Long-Term Ammonia Losses from Hay Fields.

Enhanced-efficiency nitrogen (N) fertilizers are purported to reduce N leaching and volatilization losses to the environment, and there is a plethora of short-term (2 weeks or less) monitoring studies that support these claims. However, it is less clear if the N-saving fertilizer technologies continue working over the longer term. As part of a larger study, ammonia volatilization was monitored in fertilized plots (18.6 m²), located in four different North Florida hay fields, composed of either Cynodon dactylon (L.) Pers. or Paspalum notatum Flüggé. Five N fertilizer treatments were tested as follows: 1) control with no N fertilizer (CTL), 2) uncoated urea (UCU), 3) urease inhibitor urea (UIU), 4) polymer-coated urea (PCU), and 5) Class AA biosolids (BIO). Biosolids were applied May, 2016 at 214 kg total N ha^-1 per season, while the urea fertilizers were split applied in 71 kg ha^-1 increments (initially in May and following each hay cutting, or 285 kg N ha^-1 per season). Open-chamber ammonia traps (one per replicated plot, n=3) were employed. Each week, acid bottles with wicks were exchanged and solution + wick were extracted with 2M KCl solution and analyzed for ammonium-N. Ammonia volatilization response was similar among locations and forage species. Greatest short-term (within a week of N applications) volatilization losses were from UCU. However, cumulative ammonia volatilization was similar among urea treatments, with losses ranging from approximately 6 to 12% of total N applied, while the BIO treatment losses were from 4 to 6% of total N applied. The UCU and UIU ammonia release ended within two weeks following the final fertilization in September, while PCU continued release for several more weeks. These data demonstrate that longer duration field studies are required to better establish the effect urea coating technologies have on ammonia emissions and the global N cycle.