Ammonia losses from urea applied to winter wheat over four consecutive years and potential mitigation by urease inhibitors

Urea is not only the most important mineral nitrogen (N) fertilizer worldwide, but it is also the mineral N fertilizer with one of the highest potential for ammonia (NH3) losses. The European emission inventory guidebook estimates an average loss of 16% of the applied urea as NH3. For mitigating NH3 losses from urea, the best option would be to immediately incorporate the fertilizer. However, the addition of a urease inhibitor (UI) represents a potent alternative. In a multi-year experiment from 2002 to 2005, 17 measurement periods were conducted in winter wheat (Triticum aestivum L.) and on bare soil in Southern Germany to evaluate the extent of NH3 losses following the application of urea and to determine the mitigating effect of urease inhibitors. In all measurement periods, 80 kg N ha(-1) as urea without or with the UI N-(n-butyl) thiophosphoric triamide (nBTPT) 0.3% w/w or N-(isopropoxycarbonyl) phosphoric acid triamide (IPAT) 0.4% w/w were applied. For 6-24 d following fertilizer application, NH3 emissions were continuously measured using a dynamic chamber system. Generally, low NH3 emissions were detected from urea, varying between 0.1 and 2.7% of the N applied to winter wheat and between 2.6 and 16.3% of the N applied on bare soil. Addition of the UIs IPAT and nBTPT had a significant effect on the course of NH3 emissions and reduced losses on average by 32% and 24%, respectively.