Organic matter fractions in a toposequence of six soils in the state of Rio de Janeiro, Brazil

The influence of topographical position on organic matter fractions was stu died in tropical soil toposequence in the campus of Universidade Federal Ru ral do Rio de Janeiro, State of Rio de Janeiro, Brazil. Six soil profiles w ere selected for the study, two at the shoulder position (Typic Kannapludal f, profiles 1 and 2), one on backslope (Typic Kannapludalf, profile 3), two on footslope (Fragiaquult, profiles 4 and 5) and one on the tooslope posit ion (Mollic endoaquent, profile 6). These soils have lower content of organ ic carbon. The main organic fractions modified through all water flux in th e toposequence were free fulvic acids and fulvic acids. Organic matter was correlated with soil properties, namely soil color, bulk soil density, tota l porosity, Ca2+, K+, Na+ and H+ content, and CEC. At the slope position, t he major pathway of organic matter humification was the herance pathway.