SOIL-LANDSCAPE RELATIONSHIPS IN A TOPOSEQUENCE DEVELOPED FROM BASALTIC PARENT MATERIAL

Abstract

Variations in soil attributes depend on the soil position in the landscape and drainage, erosion, and deposition processes. This study aimed to evaluate the soil physical and chemical properties, in a toposequence developed from basaltic parent material, in Batatais, São Paulo State, Brazil. The area presents a flatter topography and altitude ranging from 740 m to 610 m, in a basalt-dominated region. The experiment was carried out along a transect of 3,000 m from the top downwards. The geomorphic surfaces were identified and delimited according to topographic and stratigraphic criteria, based on detailed field investigations. Samples were collected along the representative side of profiles, for each geomorphic surface (GS) of the toposequence (GS I = top; GS II = hillside and transport foothill; GS III = shoulder and deposition foothill), totaling 142 samples. In addition, trenches were opened in the slope segments of the mapped geomorphic surfaces. The samples were analyzed for bulk density, texture, exchange bases (Ca²⁺, K⁺, and Mg²⁺), sum of bases, cation exchange capacity, base saturation, pH (water and KCl), SiO₂, Al₂O₃, Fe₂O₃ (H₂SO₄ attack), free Fe oxides extracted with dithionite-citrate-bicarbonate, and poorly crystallized Fe extracted with ammonium oxalate. The results showed that soils developed from basaltic parent material presented physical and chemical attributes tied to the relief shapes. The use of multivariate statistical techniques made possible to identify three different environments, which are equivalent to the three geomorphic surfaces.