Urease inhibitor reduces ammonia volatilization and increases rice grain yield under irrigation delay

Nitrogen is the most limiting element for the development of rice. However, under irrigated rice growing conditions, there is a recurrent delay in irrigation, which increases ammonia losses. Additionally, there is a gap between the effect of urease inhibitors and the delay of irrigation, affecting agronomic efficiency and rice yields. The objective of this work was to evaluate the ammonia volatilization and the grain yield of medium and short cycle cultivars when combining urease inhibitors and irrigation delay. The experiment was based on a double factorial, where factor 1 consisted of type of N fertilizer, urea and urea + N-(n-Butyl) thiophosphoric triamide (NBPT) and factor 2 consisted in irrigation establishing times: V3 (third leaf fully expanded), V3 + 7, V3 + 14 and V3 + 21 days. The experiment was conducted in 2016/17 and 2017/18. The accumulated volatilization, in the average of the irrigation times, was 7% and 4% to urea and urea + NBPT, respectively. In each day of irrigation delay, there was a grain yield loss of 158 and 83 kg day(-1) ha(-1), with urea and urea + NBPT, respectively. The grain yield loss of the short cycle cultivar due to irrigation delay was 12% larger than the one observed for the medium cycle and even larger when urea was used. Thus, the use of NBPT is a relevant strategy to mitigate the volatilization of ammonia, increase agronomic efficiency and grain yield of the crop when there is a delay in the irrigation.