The influence of topographical position on organic matter fractions was studied in tropical soil toposequence in the campus of Universidade Federal Rural do Rio de Janeiro, State of Rio de Janeiro, Brazil. Six soil profiles were selected for the study, two at the shoulder position (Typic Kannapludalf, profiles 1 and 2), one on backslope (Typic Kannapludalf, profile 3), two on footslope (Fragiaquult, profiles 4 and 5) and one on the tooslope position (Mollic endoaquent, profile 6). These soils have lower content of organic carbon. The main organic fractions modified through all water flux in the toposequence were free fulvic acids and fulvic acids. Organic matter was correlated with soil properties, namely soil color, bulk soil density, total porosity, Ca2+, K+, Na+ and H+ content, and CEC. At the slope position, the major pathway of organic matter humification was the herance pathway.
humus; organic matter fractionation; humification; humic substances
