Soil organic carbon saturation deficit under primary agricultural managements across major croplands in China

Introduction: To generate information for the effective management of soil organic carbon (SOC) sequestration in Chinese croplands, we compared the additional organic carbon (C) that can be stabilized by fine soil particles (<20 mu m) with typical fertilization practices across soil types and climate zones. Using data from 30 long-term experimental study sites across the major agricultural zones in China, we estimated stable SOC saturation deficit (SOCdeficit) under no fertilization (CK), chemical fertilization (CF), straw plus CF (S + CF), and manure plus CF (M + CF). Stable SOCdeficit was defined as the difference between potential and current SOC stabilized by fine soil particles. Outcomes: Stable SOCdeficit values varied from 51% to 82%. Soils dominated by 2: 1 clay minerals showed larger stable SOCdeficit than soils dominated by 1: 1 clay minerals under each treatment. For soils dominated by 2: 1 clay minerals, stable SOCdeficit was significantly lower under M + CF (69%) than under CK, CF, and S + CF (78-82%) treatments, and it increased with increasing mean annual temperature (<10 degrees C). In soils dominated by 1: 1 clay minerals, stable SOCdeficit was considerably lower in paddy and paddy-upland than in upland soils, suggesting that paddies effectively stabilize C inputs. Discussion: Agricultural soils in China have considerable C sequestration potential, despite decades of fertilization practices. To manage soil C sequestration and model soil C dynamics effectively, factors such as soil mineral types, fertilization, and cropland use should be considered. Conclusion: Our results demonstrated that manure addition was the best fertilization method for improving soil fertility, whereas straw return in Chinese croplands should take into account climate mitigation in future.