Map scale effects on soil organic carbon stock estimation in North China

Digital soil maps of different scales have been compiled in China, but exactly how map scale affects the estimation of regional SOC (soil organic carbon) stocks remains unclear. To test the effect, median, mean, and a pedological professional knowledge based method (PKB) were used to link soil profiles to soil maps at five scales ranging from 1:500000 to 1:10000000 for the Hebei Province. Excluding the 1:4000000 soil map, SOC stocks decreased as the map scale decreased. The estimated SOC stocks obtained using the mean were always higher than those using the median or PKB method. The changes in estimation due to different map scales and linking methods affected the process of assigning SOCD (soil organic carbon density) values to digital soil surveys. The differences in SOCD values resulted from the change in the total nonurban land area of each soil type as a result of the different methods and scales of maps used in the regional SOC stock estimation process.