Mitigation of ammonia losses from urea applied to a pastoral system: The effect of nBTPT and timing and amount of irrigation

Abstract

To investigate the effect of applying urea with or without the urease inhibitor (UI) N-(n-butyl) thiophosphoric triamide (nBTPT - trade name Agrotain®) and to assess impact of the amount and timing of irrigation on subsequent ammonia (NH3) emission, a field trial was set up on a research farm at Massey University, Palmerston North, New Zealand in December 2012. Measurements of the daily NH3 emission showed that majority of NH3 losses occurred during the first 1-3 days following urea application. Delaying irrigation for 48 hr post urea application resulted in high average NH3-N losses, at 23% and 28.3% for urea applied at 30 and 60 kg N ha-1, respectively. However, even when 5 or 10 mm of irrigation was applied 8 hours after urea application, average NH3 losses were still 11.3% and 14.4% of the N applied at 30 and 60 kg N ha-1, respectively. Our results suggest that 5 to 10 mm of irrigation/rainfall is needed very soon (<8 hr) after urea application to supress NH3 volatilisation depending on initial soil moisture contents. If this rainfall/irrigation is not guaranteed, then NH3 losses associated with standard urea application can effectively be reduced by 47% using urea treated with nBTPT. Keywords Agrotain, ammonia losses, irrigation, nBTPT, urea, volatilisation