Quantification of lithopedogenic iron oxides by diffuse reflectance spectroscopy and magnetic susceptibility for mapping purposes

Author(s)

Laércio Santos Silva

• Document type: Doctoral Thesis
• Press: Jaboticabal. 2021-01-05.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agrárias e Veterinárias. Jaboticabal
• Defense date: 2020-06-30
• Advisor: José Marques Júnior; Vidal Barrón López de Torre

Abstract

The Western Paulista Plateau (WPP) corresponds to approximately 13 million hectares (~ 50% of the state of São Paulo) and stands out in the production of citrus in the country (80% of the national production) and significant participation in the production of sugar and alcohol. The geological and geomorphological diversity of the region are the main cause for the spatial variability of Fe oxides, mainly goethite (Gt), hematite (Hm), maghemite (Mh) and Magnetite (Mt). Thus, recognizing the spatial variability of these oxides makes possible to identify the potential of agricultural areas, allowing the establishment of minimum management areas and the strategic planning of agricultural activities, minimizing environmental risks and optimizing operating costs. An alternative for developing the agricultural practices in these areas is the identification of the variability of soil attributes. Therefore, this study aimed to characterize the spatial variability of Fe oxides in WPP soils, using X-rays diffraction (XRD), diffuse reflectance spectroscopy (DRS) and magnetic susceptibility (χ). Sustained by sandstone (Vale do Rio do Peixe Formation — VRP) and basaltic (Serra Geral Formation — SG) rocks, WPP soils are distributed in three stages of landscape evolution: slightly, moderately and highly dissected. A total of 300 samples, collected at a depth of 0.0–0.2 m and representative of the geological and geomorphological compartments, were characterized by XRD, DRS and χ. The results were evaluated through spatial variability, relating the mineralogical data with the geomorphometric map, through statistical and geostatistical analysis. The lithological contrast between sandstone and basalt and the degree of dissection of the landscape control the spatial variability of Hm, Gt, Mh and Mt, in environments with low and high levels of Fe oxides. The similarity between maps obtained by conventional technique (XRD) and indirect methods (DRS and χ) highlights the efficiency and reliability of DRS and χ in the spatial characterization of soil Fe oxides in large areas, under complex soil-landscape relationships, in less time and investment cost. (AU)

• FAPESP's process: 17/01704-2 - Spatial variability of iron oxides and phosphate adsorbed in soil Western Paulista Plateau
• Grantee: Laércio Santos Silva
• Support Opportunities: Scholarships in Brazil - Doctorate