Ammonia volatilization from urea in rice fields with zero-drainage water management

Three field experiments located at Yuhang (YH), Changshu (CS), and Jiaxing (JX) Agricultural Research Stations in the Taihu region of China were conducted to elucidate ammonia volatilization (AV) during rice growing seasons through ‘zero-drainage water management’, combined with sound irrigation, rainfall forecasting and field drying. The experiment at each site had five N rates (0–360 kg N/ha in 90 kg increments). AV was measured by the continuous airflow enclosure method. Results show that AV was completed within 10–12 days after urea application. The peak values of AV rates after the first topdressing (AF1) at N360 treatment could reach 11.2, 9.0, and 8.5 kg N/ha day within 2–4 days at the YH, CS, and JX sites, respectively. It was only necessary to maintain a higher water level during the first ‘flooding–drying’ cycle after the AF1. The seasonal averages of the total AV fluxes accounted for 4.4–15.5%, 4.4–12.6%, and 4.6–10.9% of the applied urea at the YH, CS, and JX sites, respectively, suggesting that the zero-drainage water management with flooding–drying cycles was effective for controlling AV. This study also speculates that the total AV flux during the rice season was more N rates and seasons related than sites.