Agronomic effects of urease and nitrification inhibitors on ammonia volatilization and nitrogen utilization in a dryland farming system: Field and laboratory investigation

Reduction of ammonia (NH₃) emission in agricultural systems is highly important from agronomic, ecologic, and economic standpoints. We studied NH₃ volatilization from surface applied urea and SuperU^® (urea containing urease and nitrification inhibitors) and its interaction with tillage system (conventional tillage and no-tillage) in a dryland arable soil. Agronomic efficiency of the fertilizers was also assessed by measuring yield, agronomic N-efficiency, and apparent N-use of camelina (Camelina sativa L.). Results indicated significant variation between the field and laboratory experiments. Due to wet spell around the time of fertilization, cumulative volatilization was significantly lower in the field study. NH₃ emission associated with SuperU in the field study was about 45% lower than regular urea, which was attributed to a) activity of urease inhibitor delayed SuperU hydrolysis for about five days and b) a rainfall occurred four days after fertilization that likely carried more fertilizer into the soil from SuperU than urea. In the incubation study, NH₃ loss was notable and superiority of SuperU was not seen. The results suggest that just replacing urea with SuperU would not result in mitigation of NH₃ emission, but it provides a greater chance for N to enter the soil by one way or another (rainfall in our study). Our results did not show any appreciable interaction between N fertilizers and tillage systems. Application of SuperU in the first year of the study resulted in a significantly higher camelina yield and agronomic N-efficiency, but in the second year, due to unfavorable environmental condition, camelina did not grow well thus did not respond positively to N fertilization. The superiority of SuperU over urea in terms of NH₃ volatilization and agronomic efficiency may be achieved if farmers apply the fertilizer timely in accordance with weather conditions.