The accumulation and stability of soil organic matter are related to slope steepness. The relationships between steepness and the humification degree of humic acids, the charcoal fragment content and its radiocarbon age were quantitatively evaluated. Four Latosols (Oxisols) of the summit, shoulder, back slope and back/foot slope of a toposequence under pasture in a cratonic area in the southern Minas Gerais state, southwest Brazil, were used. The parent material of the Latosols was gneiss of the Precambrian complex, with an udic hydric regime and isothermic thermic regime. Samples were collected from every horizon and subhorizon of the four Latosols for chemical and physical characterization, humic acid extraction and determination of the semiquinone free radical content. Likewise, charcoal fragments were collected for gravimetric, nitrogen and carbon content quantification and radiocarbon dating. Our results show the close relationship of the accumulation and humification degree of soil organic matter in Latosol landscapes to slope steepness, whereas the quantity and radiocarbon age of charcoal fragments were related to the processes of soil genesis and soil position in the slope.
soil humic acids; soil charcoal; humification degree; EPR; 14C dating
