Vertical distribution of soil organic carbon

ABSTRACT / Understanding the vertical distributions of soil organic carbon (SOC) is key to predicting and simulating the influences of climate, global change, and human activi-ties on the terrestrial carbon cycle. SOC was measured at soil depths of 0 –10, 0 –20, 0 –30, 0 –50, and 0 –100 cm in 2473 soil profiles during China’s second national soil survey that was conducted from 1979 to 1992. SOC was spatially extrapolated for China. Mean SOC densities in the top 1 m ranged from 4.65 kg/m2 for bare ground to 17.32 kg/m2 in grassland land cover. SOC in the top 1 m of soil was esti-mated at 82.5 19.5 Pg C. The total SOC pool held in the top 10, 20, 30, 50, and 100 cm are 22%, 41%, 54%, 74%, and 100%, respectively. One of the objectives of the study is to examine the association of SOC content with climate and to estimate SOC storage in land-cover types at differ-ent soil depths. A partial correlation analysis shows that the mean annual precipitation was positively correlated with SOC content and the mean annual temperature was negatively correlated with SOC content, across all depths. The vertical distribution of SOC had a slightly stronger association with temperature than with precipitation in China. Soil is the largest terrestrial carbon (C) pools in the biosphere, storing 1.5 to 3 times more C than vegeta-tion. The uncertainties associated with estimating Soil organic carbon (SOC) is also the largest due in part to natural soil variability and lack of extensive soil sam