Rate and Frequency of Urease Inhibitor Application for Minimizing Ammonia Emissions From Beef Cattle Feedyards

Reduction of ammonia emissions from animal feeding operations is important from the perspective ofenvironmental policy and its impact on agriculture. A laboratory study was conducted to evaluate how rate and frequencyof urease inhibitor application affect ammonia emissions from simulated beef cattle feedyard manure surfaces. The ureaseinhibitor N-(n-butyl)thiophosphoric triamide (NBPT) was applied at rates of 0, 1, and 2 kg ha-1, at 8, 16, and 32 dayfrequencies, and with or without simulated rainfall. Synthetic urine was added every two days to the manure surface. Gaseousammonia was trapped by bubbling through a sulfuric acid solution using a vacuum system and analyzed for nitrogen usingautomated procedures. NBPT applied every 8 days was most effective, with the 1 and 2 kg NBPT ha-1 treatments resultingin 49% to 69% reduction in ammonia emission rates, respectively. The 8-day, 1 kg NBPT ha-1 treatments had the mostpromising benefit/cost ratios of 0.48 to 0.60. Simulated rainfall reduced the ammonia emission rates from 1% to 25% ascompared to the non-rainfall treatments, although the differences were not statistically different. The use of NBPT forreducing ammonia emissions looks promising; however, possible buildup of urea in the pen surface may require a higher NBPTapplication rate with time.