Optimizing N fertilizer rates sustained rice yields, improved N use efficiency, and decreased N losses via runoff from rice-wheat cropping systems

Reactive N in the runoff from paddy fields is considered to be the dominant contributor to the deterioration of river and lake water quality in China. However, there has been little researches on the interaction between N fertilizer rates and N losses via runoff from the paddy water during the summer rice-growing seasons. In the present study, we monitored the rice grain yield, N agronomic efficiency (AEN), and N losses via runoff from fertilizer N rate-response experiments applied to rice in the Taihu Lake region over 6 years. Total N loss via runoff averaged 19.3 kg ha−1 per rice season, corresponding to 7.1% of fertilizer N input at the regional N rate of 270 kg ha−1. Seasonal cumulative ammonium-N, organic N, and total N losses via runoff were all positively correlated with the fertilizer N rates (n = 1141, P