Effectiveness of the urease inhibitor NBPT (N-(n-butyl) thiophosphoric triamide) for improving the efficiency of urea for ryegrass production

Abstract

In a field experiment ammonia volatilization and yield response were measured when calcium ammonium nitrate (CAN), urea or urea plus 0.5% w/w N-(n-butyl) thiophosphoric triamide (U + NBPT) were surface-applied to an established perennial ryegrass sward. NBPT lowered cumulative NH3 loss from ventilated enclosures over 13 days from 8.1% of the urea N applied to 1.9% and delayed, by approximately 5 days, the time at which maximum loss occurred. Ammonia volatilization from CAN was low being less than 0.1% of the N applied. However, actual NH3 volatilization loss rates were probably underestimated due to the low air exchange rates used in the ventilated enclosures.