Soil carbon sequestration and land-use change: processes and potential

When agricultural land is no longer used for cultivation and allowed to rev ert to natural vegetation or replanted to perennial vegetation, soil organi c carbon can accumulate. This accumulation process essentially reverses som e of the effects responsible for soil organic carbon losses from when the l and was converted from perennial vegetation. We discuss the essential eleme nts of what is known about soil organic matter dynamics that may result in enhanced soil carbon sequestration with changes in land-use and soil manage ment. We review literature that reports changes in soil organic carbon afte r changes in land-use that favour carbon accumulation. This data summary pr ovides a guide to approximate rates of SOC sequestration that are possible with management, and indicates the relative importance of some factors that influence the rates of organic carbon sequestration in soil. There is a la rge variation in the length of time for and the rate at which carbon may ac cumulate in soil, related to the productivity of the recovering vegetation, physical and biological conditions in the soil, and the past history of so il organic carbon inputs and physical disturbance. Maximum rates of C accum ulation during the early aggrading stage of perennial vegetation growth, wh ile substantial, are usually much less than 100 g C m(-2) y(-1.) Average ra tes of accumulation are similar for forest or grassland establishment: 33.8 g C m(-2) y(-1) and 33.2 g C m(-2) y(-1), respectively. These observed rat es of soil organic C accumulation, when combined with the small amount of l and area involved, are insufficient to account for a significant fraction o f the missing C in the global carbon cycle as accumulating in the soils of formerly agricultural land.