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  With a total of 886 data sets obtained from the 2nd National Soil Survey of China that was completed in early 1980s,the relation of soil organic carbon(SOC) concentration to climate and site variables(soil order,texture,altitude,acidity/alkalinity and land use) in zonal soils of China was investigated.Correlation analysis indicates that surface SOC concentration is in general negatively correlated with annual mean temperature (T) and positively correlated with annual mean precipitation(P) and altitude(H).SOC concentration was also generally correlated significantly with the selected site variables(soil order,texture,altitude,acidity/alkalinity and land use) and the correlation was stronger in uh-cultivated soils than in cultivated soils.A further investigation suggested that multiple regression models with different combination of T,P and H could explain 41.5%~56.2%of the variability in surface SOC concentration for different geographical regions,while the driving variables are different. Variables of T and P determined surface SOM concentration in northern,northeastern and northwestern China.In eastern and southern China, variables of P and H are key factors regulating surface SOC concentration.Surface SOC concentration in southwestern China is determined by a linear combination of T,P and H.The ANOVA factorial model estimated that the contribution of site variables to the variation of SOC concentration was 24.7%in cultivated soils,48.5%in un-cultivated soils.……