Papers

Summary

Iron oxides such as goethite (Gt) and hematite (Hm) are essential minerals to better understand soil-landscape relationships. Soil samples were collected in three stages of dissecting the landscape of the geological formations of the Vale do Rio do Peixe (sandstone) and Serra Geral (basalt) in the Planalto Oeste Paulista (WPP), Brazil. Both iron oxides were quantified by X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS), and the results were subjected to geostatistical analysis in order to assess the usefulness of DRS in the characterization of spatial variability in Gt and Hm. The prevalence and spatial variability of Hm and Gt in soils were governed by the sandstone / basalt lithological contrast and landscape dissection. Iron oxides in the clay fraction exhibited high spatial variability over a large area and can be robust indicators of geological diversity and landscape dissection in pedoenvironments with low or high iron oxide content. Goethita had the greatest spatial variability. Based on the spatial pattern of the differences between the DRS and DRX estimates, the saturated red color in the soil made the DRS less useful for quantifying Hm in environments with a high iron oxide content. The maps indicate the sensitivity of the DRX and DRS techniques to represent the patterns of spatial variability of Hm and Gt. Gt was more sensitive to landscape dissection, while Hm was sensitive to lithology. Thus, the DRS technique is efficient in characterizing the spatial variability of these soil oxides over large areas, even considering the complex relationships between soil and landscape.