Influence of Temperature and Soil Type On Inhibition of Urea Hydrolysis by the Urease Inhibitor NBPT in Australian Soils.

Low nitrogen use efficiency of many agricultural systems causes both financial and environmental stresses. Urease inhibitors, such as N-(n-butyl) thiophosphoric triamide (NBPT) reduce the rate of urea hydrolysis and hence reduce nitrogen loss as ammonia (NH₃). The benefit of urease inhibitors for improving nitrogen use efficiency depends upon many variables including climatic, management and environmental conditions.  Whilst studies have been carried out internationally on NBPT on a range of agricultural systems, no detailed studies have been performed for dryland agricultural systems in Australia. Australia’s intensive agricultural production regions encompasses a large range of climatic conditions including temperatures higher than many of the previously studied areas, and so in depth knowledge of the influence of temperature on the ability of NBPT to inhibit urea hydrolysis is required to provide the best outcome for Australian farmers.

The paper reports on laboratory studies of the comparable reduction in urea hydrolysis in different agricultural systems (wheat soils, pasture systems, sugarcane trash) at different temperatures (5 to 45^oC) and the importance of the interactions between soil type and temperature. Results showed that on a highly organic pasture system increasing temperatures above 15^oC had less influence on NBPT efficacy than in wheat cropping soils. NBPT was unable to inhibit urea hydrolysis for a significant amount of time at high temperature (15 and 25^oC) in the organic pasture soils with complete hydrolysis by 7 days after urea application, whilst in the wheat soils urea remained for at least 10 days after application with NBPT.

 The paper discusses the importance of the soil type-temperature interaction on the efficacy of NBPT and the consequences for Australian agricultural systems.