ABSTRACT
In the face of climate change and increasing carbon dioxide (CO2) levels in the atmosphere, the global carbon cycle, soil organic carbon (SOC) sequestration, and the role of different world biomes as potential sources and sinks of carbon are receiving increasing attention (Feller and Bernoux 2008). Carbon (C) sequestration in plant and soil systems offers an opportunity for mitigating the greenhouse effect (Lal 2004) but the relationship between soil carbon stocks (CS) and carbon fixation in natural and anthropic vegetation remains one of the least studied issues. Emphasis has been placed on measurements of carbon fixation by forests or measurements of carbon emissions following land-use changes. As agriculture represents one of the major land-use systems, there is a close relationship between soil carbon (SC) capture and emissions and the allocation of land for agriculture. Many management practices can increase soil CS as well as above-ground carbon in biomass, including soil conservation practices (e.g., no-tillage, reduced tillage, terracing), incorporation of crop residues, increases in cropping intensity and fertilization, and conversion of cropland to permanent grasslands or forests. Although the Clean Development Mechanism (CDM) protocol has prioritized only above-ground carbon sequestration via afforestation and reforestation (A/R), the soil might represent an even larger carbon sink. In this respect, one of the challenges for the incorporation of agriculture into post-Kyoto agreements (after 2012) is to develop simple and effective methodologies for measuring, monitoring and verifying SC in cropping, farming and land-use systems.
