The topographic conditions controls many hydrological, geomorphological and pedological processes, affectting the solar radiation, pluvial precipitation, superficial water flow, evaporation, soil moisture and vegetation types, among others. Topographic properties derived from a digital elevation model were used to explain the differentiation between soils with an argillic horizon in the region of ''Mar de Morros'' in the northwestern State of Rio de Janeiro. Eight soil profiles (four Red Argisols and four Red-Yellow Argisols) developed from noritic granulites, in the municipalities of São José de Ubá and Itaperuna, were studied. The topographic data of each soil profile (elevation, slope, aspect, curvature plan and profile, solar radiation and combined topographic index) were extracted using a 7 x 7 pixel window, with the profiles in the center. Argisols on slopes facing northwest and northeast receive most solar radiation (warmer and drier) and for this reason are red, eutrophic and have no oxic horizon, whereas soils on slopes facing southeast (relatively cold and wet) are yellowish-red, dystrophic and have an oxic horizon. The solar radiation, slope and aspect are the topographic attributes that differ between the soils profiles. The topographic properties analyzed by multivariate techniques were effective to distinguish eutrophic Red Argisols from dystrophic Red-Yellow Argisols, except for P7 (PVe). Studies on the influence of solar radiation on pedogenesis under tropical conditions are scarce, and although less active in tropical regions directly determined the soil differentiation of the studied area.
argillic horizon; pedogenesis; digital elevation model
