Effect of I- and S-type granite parent material mineralogy and geochemistry on soil fertility: A multivariate statistical and Gis-based approach

Abstract

This study provides new insights into the effects of a parent material on inherent soil fertility. We describe the mineralogy and geochemistry of I- and S-type granites and their effect on soil fertility under similar environmental conditions in Borborema Province, NE Brazil, using standard mineralogical, geochemical and soil analyses as well as multivariate analysis and geographic information system approaches. We hypothesized that soils derived from I-type granites will develop higher natural fertility than those derived from S-type granites. The mineralogy and chemistry of the two different granitic parent materials have a profound effect on soil fertility. The S-type and I-type granites have different mineralogical compositions: the S-type granites have higher concentrations of silica, and the I-type granites contain larger concentrations of mafic and accessory minerals, mainly amphibole and apatite. Geophysical field measurements show different magnetic susceptibilities: for example, the I-type granites have substantial higher magnetic properties than the S-type granites. Soils derived from the I-type granites have higher natural fertility than soils derived from the S-type granites. Principal component, cluster and discriminant analyses (95% accuracy) were effective tools to discriminate among soils developed from different granites. Spatial distribution maps are suitable soil fertility management tools to guide and support soil fertility management decisions for improved soil- and crop-specific fertilization. These findings have wider implications in large parts of the tropics (South America, sub-Saharan Africa, India, SE and East Asia and Australia), which are underlain by igneous and metamorphic rock types, including S- and I-type granites, and where effective management tools are needed to increase the nutrient use efficiencies for increased productivity of food, fodder and energy crops.