Depletion and Restoration of Carbon in the Pedosphere(<Special Issue>International Symposium: Challenges to Soil Degradation Towards Sustaining Life and Environment, Tokyo Metropolitan University Symposium Series No.2, 2009)

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Food insecurity, affecting more than 1 billion people worldwide, and the risks associated with the projected climate change are among the serious global issues that must be addressed. The terrestrial biosphere in general and world soils in particular, have been sources of greenhouse gases throughout human history, but especially since the beginning of settled agriculture. Most agricultural soils have lost 25% to 75% of their original soil organic carbon (SOC) pool, with a technical sink capacity of 30 to 40Mg C/ha over a 40- to 50-year period. The magnitude of C depletion is exacerbated by soil degradation caused by erosion and other physical (compaction, drought) and chemical (salinization, acidification, nutrient imbalance) processes. Conversion to restorative land use and adoption of recommended management practices that create positive C and nutrient (N, S, P) budgets would enhance the SOC pool while also improving soil quality and the agronomic productivity. Estimates of the technical potential of C storage in the terrestrial biosphere correspond to a reduction in atmospheric CO_2 in the range of 50 to 100ppm over about 100 years.