The Effect of Urease Inhibitor NBPT on Ammonia Volatilization Loss from Urea Fertilizer: A Meta-Analysis.

The urease inhibitor N-(n-butyl) thiophosphoric triamide, after converted to its analog N-(n-butyl) phosphoric triamide (BNPO), slows the urea hydrolysis and reduces the potential for ammonia (NH₃) volatilization loss. The potential for loss is dependent on soil and environment conditions such as soil pH, soil moisture, temperature, and amount and time of rainfall after fertilizer application. A meta-analysis was done using 34 laboratory and field studies to compare NH₃ volatilization loss from urea and urea treated with NBPT. The regression analysis indicated that after 42 days of treatment application the cumulative NH₃ volatilization loss from urea and urea treated with NBPT was of 23 and 9%, respectively (a reduction of approximately 60% in loss). In addition to reducing cumulative losses, the use of NBPT delayed the NH₃ losses. For urea, 75% of total cumulative loss happened by 4 days after treatment application; while for urea treated with NBPT it happened by 8 days after treatment application. Even with NH₃ volatilization loss being dependent on environment and management factors, in all studies analyzed urea treated with NBPT presented lower losses than urea. Among several parameters, soil pH and moisture at the time of fertilizer application seems the main factors determing NH₃ volatilization loss potential. The results from this meta-analysis indicated that, when conditions favor loss, treating urea with NBPT is effective in reducing NH₃ volatilization loss.