Study of Crop-residue Return on Emission Reduction and Soil Carbon Sequestration Potential in China

As an important source of gaseous pollutants and particulate matters with significant impacts on global atmospheric chemistry and global climate change, Crop-residue burning contributes to the extremely severe and persistent haze pollution suffered by millions of Chinese people. Instead of crop-residue burning, returning crop residues to cropland can simultaneously mitigate emissions and increase soil organic carbon (SOC), which demands further spatially explicit impact assessments. Here we generated the percentage of crop residues burned in the fields and returned into cropland in 7 large regions in China. To calculate the pollutant emissions of crop-residues burning, we used grass valley ratios and emission factors, with the yields of crop residues from different crop species at different burning ratios in different agricultural regions from 2000 to 2010. Results showed that annual emissions of gaseous pollutants and particulate matters were estimated to be 149.89 Tg CO2, 0.16 Tg NOx, 0.06 Tg SO2, 1.23 Tg PM2.5 and 0.77 Tg PM10 respectively, and North, Central and Northeast China were top three contributors of agricultural regions. Based on EPIC model, which was optimized and validated using the database of long-term observation in Yucheng Station (YCS) and Qianyanzhou Station (QYZ), we stimulated a 10-year spatially explicit topsoil organic carbon density dynamics to estimate SOC sequestration potential of crop-residue return in cropland of China. The enhanced SOC from converting crop-residue burning to crop-residue return was estimated to be 24.46 Tg C yr-1, equivalent to 1.1% of the China's total carbon emission by fossil fuel. The maximum and the minimum increase of topsoil organic carbon density were in dryland of North China and paddy-fields of South China respectively.

Key Words: Agro-ecosystem