Pedogenesis in a karst environment in the Cerrado biome, northern Brazil

Karst terrains in tropical regions are object of few studies on soil properties and pedogenesis. In this study, soils pedogenesis was evaluated in a karst environment in the Cerrado biome, northern region of Brazil. The assumption is that even in the Cerrado conditions the characteristics of the soils are similar to other limestone soils in arid and semi-arid climates. Six soil profiles along a toposequence were sampled in trenches located at the summit (P1), shoulder (P2), backslope (P3), footslope (P4) and toeslope (P5 and P6) positions. The profiles were described, and their morphological (macromorphology and micromorphology), physical, chemical, mineralogical and organic matter attributes analyzed. The soils were classified as Calcic Luvisol (P1), Calcaric Eutric Cambisol (P2), Haplic Kastanozem (P3), Calcic Pellic Vertisol (P4), Orthofluvic Gleyic Calcaric Eutric Fluvisol (PS), Orthofluvic Calcaric Eutric Fluvisol (P6). Melanization and calcification are the main pedogenic processes, and they are controlled by the nature of parent material and the landscape position of the soil profile. The profiles P1, P2 and P3, at footslope and toeslope, show higher values of weathering ratios, which indicates the presence of clay minerals with a higher SiO2/Al2O3 ratio. They also have the highest amounts of CaCO3 which are associated with precipitation and neoformation of calcite. Although soils in the Cerrado biome are mostly highly weathered and with low natural fertility, the soils in the study area show accumulation of carbonates, high levels of exchangeable calcium and magnesium, pH values and base saturation that are associated with specific pedo-environments. The combination of the soil forming factors parent material and karst terrain controlled the dynamics of carbonates, leading to their accumulation in soils, regardless of the regional climatic conditions of the Cerrado biome.