O papel da litologia nos atributos fisicos, químicos e mineralógicos dos Solos Perférricos do Brasil

Abstract

In Brazil, the occurrence of soils with Fe2O3 levels above 360 g kg-1, classified as perferric in the Brazilian Soil Classification System, is still little known, restricting the profiles collected and classified to ten different parent materials. For this study, 33 profiles of the perferric soils described in EMBRAPA surveys, theses, dissertations and articles published in reviews were selected. In general, these soils have a large number of particles grouped in the fine fractions, with more than 50% of the profiles framed as clay or silt-loam. These soils are acidic, with an average pH value in H2O of 5.37, with an average balance of loads near zero and with a CEC (Cation Exchange Capacity) highly dependent on organic matter. The dystrophy is a common characteristic, being the result of either an intense weathering or even of soils that originate from already poor rocks in soluble bases.Regarding the chemistry of the clay obtained by the sulfuric attack, the soils are deficient in silica and moderately poor in aluminium. Perferric soils, independent of their parent material, tend to physical and chemical homogenization of their attributes. The lithological control is expressed mainly in developed soils of itabirite, jaspilites and ferruginous duricrusts. In these rocks, although the pedogenesis is incipient, the soils are already perferric. In the other lithotypes, such as basalt, gabbro and tuffs, the perferric character is associated with the weathering action over time, where leaching of the bases and silica and relative enrichment in iron occurs.