P400-TH EVALUATION OF THE CARBON STORAGE CAPACITY FOR A GRASSLAND

Soil organic matter (SOM) is actually of great environmental interest as the amount of organic matter stored in soils represents one of the largest reservoirs of organic carbon on the global scale (Schlesinger, 1995). As a matter of consequence, any change in soil carbon quantity may affect atmospheric CO2 concentration. Therefore carbon dioxide sequestration in plant and carbon storage in soil and biomass could be considered as a complementary solution against the increase in concentration of gases responsible for climate change. The mean residence time of SOM was observed to increase with soil depth (Rumpel et al., 2002), but limited information exists about the composition of stabilized OM. However in order to understand the mechanisms of OM stabilization in soils with depth it is necessary to characterize its structure and origin. Four horizons from the same profile of a soil located in the vicinity of Poitiers in France (INRA Lusignan, ORE Prairie) were studied. Global characterizations were realized using IR spectroscopy (Figure 1), elemental analysis and ATD/ATG. OM amount decreases slightly with depth (1,8 % at 0-30 cm and 1,1 % at 80-120 cm) but stays relatively high. The granulometric fractionation indicates a silty soil in which clays accumulate with depth