Soil carbon stocks, carbon dioxide sequestration and tillage techniques

C sequestration via agricultural soils can be accounted for, under Article 3.4 of the Kyoto Protocol, provided that specific measures are implemented. Sound cropland management can play a positive role in mitigating GHGs emissions from other sources, and carbon dioxide in particular, through a decrease of soil organic carbon (SOC) losses, an increase of organic material inputs or combining these two options. Literature data estimate about 1,500 Gg SOC to 1 m depth (Eswaran et al., 2000), in comparison with 4,000 Gg C of fossil fuels, indicating SOC as the largest sink of C after fossil fuels. Vegetation (600 Gg) and atmosphere (760 Gg) store considerably less C than soils.Carbon sequestration can occur through a reduction in soil disturbance, since more carbon is lost as CO2from tilled soils in comparison with reduced or sod-seeding systems: no tillage systems may absorb on average 0.7-1.4 t CO2ha-1yr-1(INRA 2002, ECCP 2003).This paper compares the effects of conventional tillage and sod-seeding on SOC, in a two-years rotation long term field experiment (durum wheat-sunflower 1994-01; durum wheat-corn 2002-06).