ABSTRACT
Soil organic matter (SOC) has long been recognized as a primary soil property with an essential role in soil conservation and sustainable agriculture (Johnston, 1994). SOC participates prominently in the global carbon cycle by serving as a repository that regulates the amounts that transfer annually among land, atmosphere and oceans. The degree of this regulation, however, is subject to management. Soils have acted as net sources of atmospheric C 0 2 during the conversion of forests and grasslands to agriculture. The Intergovernmental Panel on Climate Change (IPCC) (Cole et al., 1996) estimates losses from cultivated soils to have been 55 Pg (including 11 Pg from wetland soils). Similar estimates were reported by Scharpenseel (1993) and Houghton (1995). There is increasing scientific evidence, however, that soils can serve as net sinks of atmospheric C 0 2 when carbonsequestering practices are applied to agricultural soils or when native vegetation is allowed to return in agricultural land of marginal quality.
