Reducing NH3 Emissions From Australian Agriculture with the Urease Inhibitor NBPT.

Nitrogen fertilizer use in Australia is estimated at 972 Gg N per annum. Fertilizer N use efficiency worldwide is low; as low as 50% in some intensively managed agricultural systems. Urea is a commonly used nitrogen fertilizer, however, urea hydrolyses rapidly to ammonia in soil and this can lead to large losses through NH₃ volatilisation, reaching in extreme cases up to 70% of the applied N. Losses of N as NH₃ from sugarcane trash can range from negligible to almost 40% of applied N, depending upon climatic conditions. Urease inhibitors, such as N-(n-butyl) thiophosphoric triamide (NBPT) reduce the rate of urea hydrolysis and are designed to reduce NH₃ emissions. However the efficacy of the products depends upon many uncontrollable factors such as climatic and environmental conditions. 

The paper reports on laboratory chamber studies on Australian agricultural systems (sugarcane trash, wheat soils) carried out to determine the extent of reduction in NH₃ emissions as a result of using NBPT under continuous flow systems under different temperatures. The results showed that NBPT reduced the peak NH₃ emissions that occurred soon after fertilizer application and that temperature and environmental conditions (eg. soil type, plant residue) influenced the extent of reduction. On sugarcane trash the peak of NH₃ emissions from urea fertilization occurred over 8 and 12 days after fertilization at 25 and 33^oC respectively, with emissions after these days similar for the urea and urea + NBPT treatments. NBPT reduced NH₃ emissions by 55 and 39% over 21 days at 25 and 33^oC respectively. In a wheat cropping clay loam soil at cooler temperatures (15^oC) the peak NH₃ emissions from urea occurred over 16 days after fertilization and NBPT reduced these emissions by 79%. NBPT shows promise for improving the N-use efficiency of urea fertilizer in some Australian agricultural industries.