Re-estimating NH3 Emissions from Chinese Cropland by a New Nonlinear Model

Ammonia (NH3) released to the atmosphere leads to a cascade of impacts on the environment, yet estimation of NH3 volatilization from cropland soils (V-NH3) in a broad spatial scale is still quite uncertain in China. This mainly stems from nonlinear relationships between V-NH3 and relevant factors. On the basis of 495 site-years of measurements at 78 sites across Chinese croplands, we developed a nonlinear Bayesian tree regression model to determine how environmental factors modulate the local derivative of V-NH3 to nitrogen application rates (N-rate) (VR, %). The V-NH3 -N-rate relationship was nonlinear. The VR of upland soils and paddy soils depended primarily on local water input and N-rate, respectively. Our model demonstrated good reproductions of V-NH3 compared to previous models, i.e., more than 91% of the observed VR variance at sites in China and 79% of those at validation sites outside China. The observed spatial pattern of V-NH3 in China agreed well with satellite-based estimates of NH3 column concentrations. The average VRs in China derived from our model were 14.8 +/- 2.9% and 11.8 +/- 2.0% for upland soils and paddy soils, respectively. The estimated annual NH3 emission in China (3.96 +/- 0.76 TgNH(3).yr(-1)) was 40% greater than that based on the IPCC Tier 1 guideline.National Natural Science Foundation of China [41201077, 51168047]; Research Fund for the Doctoral Program of Higher Education of China [20120001120129]; 111 Project [B14001]SCI(E)EIPubMedARTICLEzhouf@pku.edu.cn; yangcl227@163.com2564-5725