Effect of urease inhibitors on urea hydrolysis and ammonia volatilization

Two laboratory incubation experiments were conducted to study the effects of the urease inhibitors hydroquinone (HQ), phenyl phosphorodiamidate (PPDA), and N-(n-butyl) thiophosphoric triamide (NBPT) in retarding the hydrolysis of urea, in the evolution of mineral N, and in reducing NH3 loss through volatilization, under aerobic and waterlogged conditions, both at 25-degrees-C. NBPT generally exceeded PPDA and HQ in the ability to delay urea hydrolysis and NH4+ accumulation under aerobic conditions, whereas PPDA retarded these activities more effectively under anaerobic conditions. HQ was less effective than the other two urease inhibitors. Under aerobic conditions, 20% of the applied urea was lost through NH3 volatilization after 5 days in the system without an inhibitor. With the addition of HQ and PPDA, the voltalization was delayed by 1 day but not eliminated. NBPT effectively decreased the NH3 loss, from 20 to 3% of the applied urea. A more severe N loss (40 occurred in the waterlogged system. HQ had little effect on NH3 volatilization. PPDA decreased the NH3 loss from 40 to less than 20% of the applied urea. The effectiveness of NBPT decreased under anaerobic conditions. It was concluded that urease inhibitors can reduce NH3 volatilization following the application of urea. However, environmental conditions might have an important influence on the effectiveness of these inhibitors.