Mineralogy of Brazilian Vertisols: influence on soil properties, genesis and classification

• Grant number: 20/16446-1
• Support Opportunities: Regular Research Grants
• Start date: November 01, 2021
• End date: April 30, 2024
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Physical Geography
• Principal Investigator: Sheila Aparecida Correia Furquim
• Grantee: Sheila Aparecida Correia Furquim
• Host Institution: Instituto de Ciências Ambientais, Químicas e Farmacêuticas (ICAQF). Universidade Federal de São Paulo (UNIFESP). Campus Diadema. Diadema , SP, Brazil
• Associated researchers: Caroline Delpupo Souza ; Gabriel Ramatis Pugliese Andrade ; Grace Bungenstab Alves ; Irina Kovda ; José Coelho de Araújo Filho ; Valdomiro Severino de Souza Júnior

Abstract

Vertisols are soils characterized by clayey texture and dominance of smectite minerals, which allow for a high coefficient of expansion and contraction of the soil mass in wetting and drying conditions. Soil morphological, physical and chemical characteristics of Vertisols are closely related to the types and amounts of smectite and other clay minerals, but their identification and characterization are commonly general and qualitative in the literature, avoiding a deeper knowledge about the relationship between the minerals with the soil properties, genesis and classification. Thus, the objective of this project is to investigate the qualitative and quantitative characteristics and mechanisms of genesis of clay minerals in Brazilian Vertisols, in order to better understand the role of clay mineralogy in the manifestation of the vertic and chemical properties, as well as in the formation, degree of development and classification of these soils. Representative profiles of Brazilian Vertisols will be studied through morphological descriptions, physical analyses (particle-size and coefficient of linear extensibility-COLE) and chemical analyses (pH, electrical conductivity-EC, exchangeable cations, CEC) of bulk soils (total samples). Mineralogical analyses will be carried out in the coarse (2-0.2 µm) and fine clay (<0.2 µm) samples, including qualitative and quantitative (software Newmod) X-Ray Diffraction, Inductively Coupled Plasma Spectroscopy (ICP), Scanning-Transmission Electron Microscopy (STEM), coupled with elemental analysis (EDS, HAADF) and Mossbauer Spectroscopy. These methods will allow for the identification, quantification and chemical characterization of pure and mixed-layered clay minerals, including the recognition of different species of smectites and other clay groups. The combination of all the results should allow for a better understanding of the role of the mineralogy and the possible existence of a smectite threshold in the generation of vertic properties, the identification of autigenic and allogenic clay minerals and the comprehension of their specific process of genesis (transformation or neoformation) and, finally, the weathering rates and their relationship with formation of the clay minerals and the soils themselves. Also, based on the study of the detailed clay mineralogy of Vertisols, it will be possible to evaluate the common assumption in the literature that they are homogeneous and immature soils, which may permit a revision of their classification criteria. (AU)