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(<20μm)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(SOC_(deficit))under no fertilization(CK),chemical fertilization(CF),straw plus CF(S+CF),and manure plus CF(M+CF).Stable SOC_(deficit)was defined as the difference between potential and current SOC stabilized by fine soil particles.Outcomes:Stable SOC_(deficit)values varied from 51%to 82%.Soils dominated by 2:1 clay minerals showed larger stable SOC_(deficit)than soils dominated by 1:1 clay minerals under each treatment.For soils dominated by 2:1 clay minerals,stable SOC_(deficit)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°C).In soils dominated by 1:1 clay minerals,stable SOC_(deficit)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.