Ammonia emission from manures treated with different rates of urease and nitrification inhibitors

Urease inhibitors have been successfully used to reduce ammonia (NH3) emission from urea-based fertilizers. However, studies on its effectiveness with manures have produced inconclusive results. Field and greenhouse studies were conducted to investigate the effectiveness of different rates of urease [N-(n-butyl) thiophosphoric triamide; NBPT] with and without nitrification inhibitor (NI) in reducing NH3 emission from surface-applied liquid pig manure (LPM) and solid beef manure (SBM). Ammonia emission was measured with acid-charged discs at seven dates for 28 d. Total NH3 emission (% of applied N) ranged from 4.3% to 8.2% in untreated LPM and 8.2% in untreated SBM. The corresponding NH3 emission was 6.8%–7.4% in LPM treated with NBPT, 5.0%–12.3% in LPM treated with NBPT + NI (double inhibitor; DI), and 6.0%–10.8% in SBM treated with DI. In the field study, NH3 emission was not significantly different between either LPM or SBM treated with and without DI. In the greenhouse, NBPT did not significantly reduce NH3 emission from LPM, whereas DI applied at a lower rate significantly increased NH3 emission from LPM. In conclusion, addition of NBPT to manure did not have any significant environmental benefit, whereas a combination of NBPT and NI increased NH3 emission from manure.