Modeling ammonia volatilization over Chinese croplands

Ziyin Shang1, Feng Zhou1, Shuoshuo Gao 1, Yan Bo1, Philippe Ciais 2, Kentaro Hayashi 3, James Galloway 4, Dong-Gill Kim 5, Changliang Yang 6, Shiyu Li 6, Bin Liu 6

1 Sino-France Institute of Earth Systems Science, Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing, 100871, P.R. China, Email: [email protected]

2Laboratoire des Sciences du Climat et de l’Environnement, CEA CNRS UVSQ, 91191 Gif-sur-Yvette, France

3Carbon and Nutrient Cycles Division, National Institute for Agro-Environmental Sciences, 3-1-3, Kannondai, Tsukuba, Ibaraki 305-8604, Japan

4Environmental Sciences Department, University of Virginia, Charlottesville, Virginia 22904, USA

5Wondo Genet College of Forestry and Natural Resources, Hawassa University, PO. Box 128, Shashemene, Ethiopia

6Research Institute of Engineering Technology, Yunnan University, Kunming, 650091, P.R. China

Abstract

Ammonia (NH3) released to the atmosphere leads to a cascade of impacts on the environment, yet estimation of NH3 volatilization from cropland soils (VNH3) in a broad spatial scale is still quite uncertain in China. This mainly stems from non-linear relationships between VNH3 and relevant factors. Based on 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 VNH3 to nitrogen application rates (Nrate) (VR, %). VNH3-Nrate relationship was non-linear. VR of upland soils and paddy soils depended primarily on local water input and Nrate, respectively. Our model demonstrated good reproductions of VNH3 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 VNH3 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 TgNH3·yr-1) was 40% greater than that based on the IPCC Tier 1 guideline.