Effects of NBPT urease inhibitor on ammonia volatilization in paddy fields with wheat straw application

While ammonia volatilization is the main mode of nitrogen loss in paddy fields, urease inhibitors are known to effectively inhibit urease activity, delay urea hydrolysis and reduce ammonia emission. Urease inhibitors have, however, not been widely applied in paddy fields. In this study, the effects of NBPT urease inhibitor on the dynamic changes in urea hydrolysis and ammonia volatilization in wheat-straw incorporated gley paddy soils in Taihu Lake region were investigated via the dynamic chamber method. Results showed that ammonia volatilization mainly occurred during basal and tillering fertilization periods. While the highest ammonia volatilization was at basal fertilization stage, the lowest was at booting fertilization stage. Ammonia volatilization mainly occurred within three days after fertilization. Applying NBPT one day before fertilization significantly retarded urea hydrolysis, delayed occurring time and decreased value of NH₄⁺-N peak and reduced rate and amount of ammonia volatilization of surface water. After basal and tillering fertilization, urea hydrolysis ended within 2~3 days after fertilization, NH₄⁺-N and ammonia volatilization peaks occurred on the second day under non-NBPT treatment. Peak values of NH₄⁺-N of basal and tillering fertilization were 132.3 mg·L^-1and 66.3 mg·L^-1, respectively. Also ammonia volatilization peak values were 15.6 kg·hm^-2·d^-1 and 10.4 kg·hm^-2·d^-1, respectively. Under NBPT treatment, however, the peak of NH₄⁺-N occurred 4 days after fertilization after which it dropped to 70.7 mg·L^-1 and then to 51.6 mg·L^-1. After 4 days of fertilization, ammonia volatilization peak dropped to 4.7 kg·hm^-2·d^-1 and then to 2.6 kg·hm^-2·d^-1. Total ammonia volatilization dropped from 73.3 kg(N)·hm^-2 (24.4% of applied N) to 34.5 kg(N)·hm^-2 (11.5% of applied N) after NBPT application, a drop of 53%. NBPT application in wheat-straw incorporated paddy fields significantly reduced ammonia volatilization by delaying urea hydrolysis. It was recommended that NBPT urease inhibitor could be used as nitrogen fertilizer additive to inhibit ammonia loss in paddy fields.