Fig. 5. Relationships between the soil organic C (SOC) pools in MLRAs and site variables. Mean values of the SOC pool, drainage class index, and slope percentage were calculated using the MLRA-taxonomic approach. The data of drainage class and slope are from the pedon records in the attribute data table and the areas for area-weighted means are derived from the attribute table associated with the taxon-land use-MLRA theme. Drainage class 0, 1, 2, ...., 6 are assigned for very poorly, poorly, somewhat poorly, moderately well, well, somewhat excessively, and excessively drained, respectively.