Ammonia volatilization and nitrogen balance after topdressing fertilization in paddy fields of Taihu Lake region

Ammonia volatilization, N fertilizer fate and soil residual nitrogen at different rice growth stages were investigated via continuous air-flow enclosure method and field ¹⁵N micro-plot experiment in gley paddy soils in Taihu Lake region. Results showed that ammonia volatilization occurred within one week and peaked in 1~2 days after fertilization. The rate of ammonia volatilization changed with NH₄⁺-N concentration in surface water. Ammonia volatilization loss from surface water respectively accounted for 16.7% and 6.3% of fertilizers applied at tillering and booting stages. Nitrogen use efficiency of rice plant was 36.7% and 49.6% of applied fertilizers at tillering and booting stages, respectively. This was mainly due to less ammonia volatilization after booting fertilization, which was more readily transferred to grains. In the two topdressing fertilization, apparent rate of nitrogen loss were 52.8% and 40.7% of applied N fertilizer respectively. About 10.6% of applied N fertilizer remained in the soil, which was mostly concentrated in the 0~20 cm soil layer. This showed that fertilization in booting stage could improve N use efficiency and reduce N loss. This was because of low ammonia volatilization loss and high utilization of fertilizers by grain of panicles during this period.