Carbon in soils occurs in organic and inorganic forms. The inorganic carbon is derived from weathered bedrock, is relatively inert and constitutes little to the carbon cycle. Soil organic carbon is derived from plant and other decaying matter and is a significant part of the carbon cycle. About 10% of the atmospheric carbon cycles through soils each year. Soil organic carbon represents the largest terrestrial carbon pool, amounting to about two to three times the net size of the biomass pools. Carbon sinks may be explained by changes in above-ground biomass on seasonal to decadal timescales, but soil organic carbon stocks become significant on longer timescales, and can be a significant source at all timescales after disturbances.
% Carbon in soil; Mineral soil bulk density to 30 cms and 1m Peatlands total depth of profile, area and location