Ammonia emissions from paddy fields are underestimated in China

Highlights: • 17.7% of the N fertilizer applied to paddy fields lost through NH₃ emissions. • The measured NH₃ emission was 33.1% higher than previously reported. • Non-linear response of NH₃ emissions to N fertilizer rate was found. • Total NH₃ emissions from paddy fields were 1.7 Tg N yr⁻¹ in 2013 in China. Excessive nitrogen (N) fertilizers are often used in China, and a large proportion of the N can be lost as ammonia (NH₃). However, quantifying the NH₃ emission from paddy fields is always affected by large uncertainties due to different measuring methods and other factors such as climate. In this study, using a standardized method, we measured the NH₃ emissions in three typical annual rice cropping systems: single rice, double rice and rotation with other crops. The measurements were conducted for 2 years with a total of 3131 observations across China. Results showed that NH₃ emissions accounted for 17.7% (14.4–21.0%) of the N applied under current farm practice, which was 33.1% (10.6–52.6%) higher than previous estimates. Nitrogen application rate was the dominant factor influencing NH₃ emission rate, which exponentially increased with the N fertilizer rate (p 001). Total NH₃ emissions from paddy fields were estimated at 1.7 Tg N yr⁻¹ in 2013 in China, several times the amount of N lost through leaching or runoff. This suggests that mitigation measures for non-point source pollution from cropland should take into account not only the N lost to water, but also to air, thereby improving air quality.