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.
Proceedings of New Zealand Grasslands Association, 2013, 75 pp. 209 - 214