Influence of vegetation type on silicon content in different subtropical soils

Soil weathering is the term that describes soil genesis, and its good visual indicators are natural vegetation cover and soil morphology. However, do the same soil types under different vegetation covers affect the degree of soil weathering? Our objective was to study two contrasting soil types under natural vegetation to discuss the degree of weathering, considering their morphology, silicon (Si) content, and fine mineralogy assemblage. Soil samples were collected in nearby Brazilian regions with Ferralsol and Regosol soils, as well as native forest and grassland areas. Soil profile, mineralogy, and chemical composition (total and available ions) were described. Both soils presented the following minerals: mica/illite, kaolinite, quartz, and cristobalite. Available Si content ranged from 6.31 to 8.76 mg kg⁻¹, and it was higher in Ferralsol than in Regosol soils but did not show dependency on the vegetation type. The total SiO₂ content ranged from 283.5 to 341.4 g kg⁻¹. The Ki index was higher in the A horizons (2.77) of Ferralsols than in Regosols. The silt/clay ratio content discriminated soil types more accurately. Although vegetation types, mineralogy effects, and Si availability were weak as factors of soil evolution under native conditions, these findings do not end the discussion about the impact of vegetation cover on soil weathering. Further studies on different soil classes are recommended, including assessments of Si content in plant tissues, to elucidate the link of vegetation and mineralogy to chemical availability.