Spatiotemporal Variation And Driving Factors Of Carbon Sequestration Efficiency In Typical Upland Agricultural Soils Of China

Soil organic carbon(SOC)is the core of soil fertility,and is closely related to the global carbon cycle.The amount of these organic C input incorporated into SOC pool however were regulated by not only the amount of C input but also the conversion rate of C input,which is hereafter named carbon sequestration efficiency(i.e.CSE)in the current study.Because the spatio-temporal differences and driving factors of the surface and deep CSE under long-term fertilization experiments in China are unclear,and also the relative contribution of different carbon fractions to the SOC is not clear.we selected 8 long-term fertilization experiments in China,and collecting the data of soil properties,climatic factors,and crop yields from the initial year to 2009/2010,the following conclusions were obtained:(1)There were significant fertilization effects on C input and ΔSOC(NPKM>NPK>CK),and significantly lower CSE in HH than the others.The variance partitioning analysis(VPA)showed more variance of CSE can be explained by edaphic factors(up to 39.7%)than other factors.Furthermore,soil available N content and pH were identified as the major soil properties explaining CSE variance.This study demonstrated key controls of soil fertility factors on soil organic carbon sequestration and informs the need to develop strategic soil management plan to promote soil carbon sequestration under long-term intensive fertilization.(2)SOC stock generally decreased with soil depth and increased with fertilizations(i.e.initial,CK<NPK<NPKM).As a result,SOC stock increases(0-60cm)was accelerated at GZL and CQ but dampened at ZZ and QY under NPK and NPKM when accounting for deep soil SOC stock changes.Regardless of OC input under different fertilizations,our model simulations supported a consistently larger CSE at 0-60cm than that at 0-20cm at GZL and CQ but lower at ZZ and QY.The key underlying driving factors for the depth-specific CSE may lie in different edaphic characteristics.These results demonstrated that both surface and deep soil can act as important soil carbon sinks particularly under combined chemical fertilizer and manure.Relative to surface soil,CSE of soil profile including deep soil horizons was elevated in intrinsically high fertility soils but dampened at poor fertility soils.Accounting for deep soil carbon changes will enable more accurate estimates of soil C sequestration capacity in cropland soils under long-term fertilizations.(3)The surface(0-20cm)SOC storage ranged from 18.5 to 48.8 t ha-1 for the 5 long-term fertilization experiments for the initial year and the 2009/2010.NPKM and NPK significantly increased SOC storage andΔSOC,and both were NPKM>NPK.For the ΔSOC,about 50%of the relative contribution from oxidized organic carbon,and the relative contribution of stable organic carbon was also about 50%under NPK and NPKM.However,there is no obvious law under CK treatment.This study will enable more accurate estimates of soil C sequestration capacity in cropland soils under long-term fertilizations,and provide scientific proof for fertilization promotion and management efficiency in typical upland soils in China...