EDAFOLOGIA, Vol. 11(2), pp. 157-170, 2004
CARBON SEQUESTRA TION RESEARCH IN BRAZILIAN SAVANNAH SYSTEMS: PROBLEMS AND RESULTS
P. BUURMAN1, R. ROSCOE1,2, F. de ALCANTARA1,3
1 Soil Science and Geology, W ageningen University, P .O. Box 37, 6700 A A Wageningen, the Netherlands 2 Present address: EMBRAPA Agropecuaria Oeste, 79804-970 Dourados MS, Brazil 3 Department of Soil Science, Federal University of Lavras, 70919-970 Lavras, Brazil
The natural abundance of 13C is a good tool to study soil organic matter dynamics in systems where the photosynthetic path of the dominant vegetation is changed. Still, considerable uncertainty remains concerning isotope discrimination during humification of C4-litter, the representativity of sites in relation to spatial variation, and procedures of humus fractionation. In the Brazilian savannah, the cerrado, humus dynamics is relatively fast and amounts of 30-40% of the native humus can be replaced within decades. It is not clear, though, whether the fractions that have not been replaced within that time span have a significantly different dynamics. The fact that a significant portion of organic matter in such soils is not extractable by the regular procedures, suggests that its turnover time may be an order of magnitude slower than that of the easily replaced fractions addressed in this paper. Any students investigating the effects of land use change on soil organic matter should be aware that equilibrium situations cannot be reached in decades or even centuries, and that the predictive value of such studies is necessarily limited, even if the correct procedures are used.