Influence of temperature and soil type on inhibition of urea hydrolysis by N-(n-butyl) thiophosphoric triamide in wheat and pasture soils in south-eastern Australia

Incubation experiments were conducted to assess the effectiveness of N-(n-butyl) thiophosphoric triamide (NBPT) for inhibiting hydrolysis of urea in three wheat-growing soils and one pasture soil in south-eastern Australia, under a range of temperatures (5, 15, 25°C). The effectiveness of NBPT decreased with increasing temperature and with increasing urease activity. In the acidic pasture soil with high urease activity (186 μg N/g soil.h) and high organic carbon content (11%), NBPT (0.1% w/w urea) had little impact on urea hydrolysis rates over all temperatures, with <1% urea remaining at Day 14. In the alkaline, wheat-cropping soils with lower urease activity (54–90 μg N/g soil.h) and lower organic carbon content (<1.5%), NBPT was able to effectively reduce urea hydrolysis over 14–15 days at 5°C and 15°C (>55% urea remaining). At 25°C in the wheat soils, NBPT slowed the rate of urea hydrolysis, but by Days 14 and 15, <2% of the urea remained. NBPT applied at a rate of 0.1% urea would be an effective tool for slowing urea hydrolysis in the wheat-cropping soils under cool-climate conditions. The delay in urea hydrolysis in the pasture soil still provides the opportunity for increased flexibility in farm management, such as irrigation scheduling.