Does 3,4-dimethylpyrazole phosphate or N-(n-butyl) thiophosphoric triamide reduce nitrous oxide emissions from a rain-fed cropping system?

Nitrification and urease inhibitors have been used to reduce nitrous oxide (N₂ O) emissions and increase nitrogen use efficiency in many agricultural systems. However, their agronomic benefits, such as the improvement of grain yield, is uncertain. A two-year field experiment was conducted to (1) investigate whether the use of 3,4-dimethylpyrazole phosphate (DMPP) or N-(n-butyl) thiophosphoric triamide (NBPT) can reduce N₂ O emissions and increase grain yield and (2) explore the financial benefit of using DMPP or NBPT in a rain-fed cropping system in south-eastern Australia. The experiment was conducted at Wagga Wagga, New South Wales, Australia with wheat (Triticum aestivum L.) iN₂012 and canola (Brassica napus L.) iN₂013. Results showed that urea coated with DMPP reduced the cumulative N₂ O emission by 34% for a wheat crop iN₂012 (P < 0.05) and by 62% for a canola crop iN₂013 (P < 0.05) compared with normal urea, but urea coated NBPT had no effect on N₂ O emission for the wheat crop iN₂012. Neither nitrification nor urease inhibitors increased crop yields because the low rainfall experienced led to little potential for gross N loss through denitrification, leaching or volatilisation pathways. In such dry years, only government or other financial incentives for N₂ O mitigation would make the use of DMPP with applied N economically viable.