Urease Inhibitor NBPT on Ammonia Volatilization and Crop Productivity: A Meta-Analysis

The urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) slows urea hydrolysis, reduces NH3 volatilization loss, and enhances N availability to plants. Even though most studies have proved the potential of NBPT-treated urea to reduce NH3 loss, the benefits to increase crop yield have been less consistent, mainly because N is not always the limiting factor. A meta-analysis was carried out to evaluate the effect of soil properties (e.g., soil pH, soil texture, soil organic C [SOC]), N rate, and NBPT concentration on NH3 volatilization loss and crop yield when comparing urea with NBPT-treated urea. Regression analysis indicated cumulative NH3 loss of 31.0 and 14.8% of applied N for urea and NBPT-treated urea, respectively, a 52% reduction in NH3 loss by using the urease inhibitor. Th e use of NBPT delayed NH3 loss. It took 4.8 and 8.3 d for 50% of the total NH3 loss to occur for urea and NBPT-treated urea, respectively. Th e meta-analyses indicated that when compared with urea, NBPT-treated urea reduced NH3 volatilization loss across all soil pH classes, soil texture classes, SOC contents, N rates, and NBPT concentrations. Th e meta-analysis indicated an average crop yield increase of 5.3% for NBPT-treated urea compared with urea. Th is trend was observed for all classes of soil pH, SOC content, and N rate, but yield increases were limited in coarse-textured soils and NBPT rates > 1060 mg kg(-1).