Spatially explicit simulation of soil organic carbon dynamics in Chinaʹs paddy soils

Paddy soils support important croplands in many parts of the world, especially in Asia, so an accurate estimation of the magnitude and dynamics of paddy soil organic carbon (SOC) stocks is critical to support adoption of appropriate soil conservation measures and development of strategies for greenhouse gas mitigation. To reduce uncertainties from upscaling spatial processes of the DeNitrification–DeComposition (DNDC) model for improving the definition of Chinaʹs paddy soils SOC stocks (0–30 cm) and their changes from 1980 to 2008, a soil polygon-based modeling method was developed by integrating DNDC with the latest 1:1,000,000 soil database, derived from 1490 paddy soil profiles collected during the Second National Soil Survey of China. The simulations demonstrated that Chinese paddy soils (0–30 cm), which cover 45.0 M ha, storaged 2.51 Pg in 1980 and 2.65 Pg in 2008 with an average sequestration rate of 5.0 Tg C year− 1. Approximately 83.3% of the paddy soils sequestrated C, while 16.1% lost C and only 0.6% were balanced over the past 28 years. There were, however, large regional differences in sequestration outcomes. Increases in paddy soil SOC stocks were found predominantly in South, Eastern and Southwest China, where topsoil SOC increased by 59.6, 56.4 and 28.3 Tg, respectively. SOC stock in Northwest and North China increased only 0.6 and 0.3 Tg, respectively, while that in Northeast China lost 0.5 Tg. Enhancement in the soil databases with higher resolution inputs should improve the C sequestration estimates of any area of interest.