Determining Ammonia Volatilization Losses From Enhanced Urea Products.

Urea can be rapidly converted via the ubiquitous enzyme urease to NH₃ gas. This gas is volatile and in extreme circumstances can account for up to 50 percent of applied N being lost to the atmosphere.  To combat this N loss, manufacturers have developed additives and specialty N fertilizer products designed to inhibit N losses and prolong the N release period.  These products include inhibitors (urease and/or nitrification) and polymer coatings.  To assess the effectiveness of these products at reducing fertilizer N loss through ammonia volatilization, a semiopen-static system using clear plexi-glass tubes, polyurethane foam sorbers, and a phosphoric acid:glycerin trapping solution was used to monitor ammonia losses from corn plots fertilized at a rate of 168 kg N ha^-1.  Two inhibitor products, two polymer coating products, untreated urea, and urea ammonium nitrate (UAN) were assessed.  Ammonia loss was measured 1, 2, 3, 5, 7, 10, 15, 20, and 25 days after application.  After 25 days, ammonia-N trapped by the polyurethane sorbers accounted for 1.0 and 2.7% of total fertilizer N applied as polymer coated urea while ammonia-N losses from inhibitor products was 2.1 and 4.8% of fertilizer N applied.  Ammonia-N losses from untreated urea and UAN was 4.4 and 3.3%, respectively.  Despite differences in ammonia-N losses, corn yields were similar between inhibitor products, untreated urea, and one of the polymer coated products.  The other polymer coated product yielded more than all other N sources except UAN.  Results suggest that the semiopen-static ammonia trapping system was effective at determining differences in ammonia-N losses arising from these different product classes.   Early-season ammonia-N losses did not consistently correspond with grain yield differences.