Climatic effect on soil organic carbon variability as a function of spatial scale

Soil organic carbon (SOC) is spatially heterogeneous. Understanding SOC variability as a function of varying scale is important for accurately estimating the SOC stock. We selected three zones in the Huang-Huai-Hai agricultural region of China to define temperature (T Zone), precipitation (P Zone) and temperature + precipitation (PT Zone) gradients, respectively. The zonal differences in SOC variability as a function of increasing scale were examined. The results demonstrated that the SOC stock varied substantially among the different zones. The coefficient of variation (CV) of the SOC stock was more elevated in the PT Zone and was influenced by scale level. The mean CV increased by 12.5%, 4.6% and 2.9% from 1C to 12C for PT, T and P Zone, respectively. Zonal SOC variability differences were not obvious at small scale, with the CV ratio consistently less than 0.003 in the three zones; however, they became detectable at higher scales (6C and 12C), with the CV ratio showing as: PT Zone > T Zone > P Zone. SOC zonal variability must be considered to reduce uncertainty for soil carbon stock estimation.