Orientation of layers of poor metapellitic rocks on genesis of latosols (Oxisols) under cerrado vegetation

Abstract

During the high intensity recconnaissance soils survey of the region under influence of Itutinga/Camargos reservoir, MG, Brazil, Una variant Latosol (LU) and Dark-Red Latosol (LE), both Oxisols, which occur in intimate geographical association, under identical conditions of relief, vegetation, climate, regional parent material and landscape position were identified. The type of orientation of layers of the parent material, by conditioning a differential moisture regime in the two systems exerts markable influence on the pedogenesis of these soils: (1) the horizontal orientation of the layers conditioned the genesis of the Una variant Latosol, having yellowish colors, lower grade of weathering-leaching, evidenced by higher values of Ki and Kr indices and lower gibbsite/kaolinite ratio, smaller solum thickness, and having higher goethite/hematite proportion: and (2) the inclined orientation of the layers conditioned under similar conditions, the formation of Dark-Red Latosol having better drainage, more weathered (higher gibbsite/kaolinite ratio and smaller Ki and Kr indices), with thicker solum, having lower Fe_o/Fe_d ratio, higher hematite/goethite proportion and, consequently, reddish colors.