Figure 6: Annual rate of the change in soil organic carbon stock (SOC) in the top 20 cm depth of soil as related to the baseline SOC levels across the study area. (a) Annual rate of SOC change from 1972 to 2007 for cropland and grassland; (b) annual rate of SOC change averaged for all land use types from 1972 to 1998 and 1998 to 2007.