Iron-bearing minerals and natural fertility of magnetic soils of Jequitinhonha Valley, Minas Gerais State, Brazil

Abstract

This study aimed at characterizing the chemical and mineralogical nature of soils derived from basic and acidic bedrocks from the Jequitinhonha Valley, Minas Gerais State, Brazil, focusing on the occurrence of magnetic minerals and its relationship with the natural fertility. The following soils were described, classified and sampled, according to the USDA Soil Taxonomy nomenclature: Typic Haplustox, Rhodic Kandiustox, Rhodic Haplustox and Typic Argiustoll. Granulometric analyzes and contents of macro and micronutrients were determined. In order to get more insights about each diagnostic soil horizon, the contents of the main metal cation oxides, specifically, iron, aluminum and manganese, were obtained by sulfuric acid digestion, and through their residual extractions with mixtures dithionite - citrate - bicarbonate and oxalate - oxalic acid. The samples were also analyzed by Mössbauer spectroscopy in an attempt to identify the main magnetic iron oxides. Maghemite (?Fe2O3) was found in all samples and magnetite (Fe3O4) was identified only for the sample Typic Argiustoll. Soils with higher magnetizations were found to have higher natural fertility.