Chemistry, mineralogy and micropedology of highland soils on crystalline rocks of Serra da Mantiqueira, southeastern Brazil

Abstract

A typical altitudinal sequence of four soil profiles from one of the uppermost areas of the Mantiqueira Highlands (Minas Gerais State, southeastern Brazil) was studied regarding physical, chemical, mineralogical and micromorphological attributes. The soils were classified as a Terric Haplosaprist, a Humic Xanthic Hapludox, a Typic Haplorthod and a Humic Psammentic Dystrudept. All soils are gibbsitic, highly acidic and distrophic, with high aluminium saturation. The high organic carbon content and coarse texture favour the occurrence of podzolization. Intense hydrolysis and mineral dissolution occur in the studied pedoenvironments, with the presence of adsorbed Al polymers and organic matter bound Al forms. Podzolization can only be confirmed with the combined analysis of soil humic fractions, Al forms and micromorphological attributes. The conspicuous presence of gibbsite is attributed to past conditions of deep weathering and saprolite formation. Closed nutrient cycling is essential for environmental sustainability due to the very low nutrient reserve of soils and deep pre-weathered saprolites. The highland subtropical environment is an important site of natural carbon immobilization in the tropics in which histic/humic horizons are the most important loci of carbon inputs.