ABSTRACT
The main source of soil organic C (SOC) is the input of organic matter via belowground and aboveground return of plant residues. Part of this input of organic C is transformed by soil biota into organic compounds of varying composition, a small part is leached as dissolved organic carbon, and the rest is returned to the atmosphere as C 02. Transformations of SOC depend upon the decomposability of the litter and the biotic activity. Organic compounds in the soil undergo successive transformation by biotic action until they are protected either physically by becoming inaccessible to microbial activity (occluded fraction) or chemically by forming strong bonds with mineral surfaces (organo-mineral complexes). Transformation of SOC into lesser or least labile forms is part of the C sequestration process.
