Clay Mineralogy of Brazilian Oxisols with Shrinkage Properties

Samara Alves Testoni,Jaime Antonio De Almeida,Luana Da Silva,Gabriel Ramatis Pugliese Andrade

doi:10.1590/18069657rbcs20160487

Abstract

ABSTRACT Shrinkage capacity (carater retratil in Portuguese) is a new diagnostic characteristic recently introduced in the Brazilian System of Soil Classification (SiBCS) to indicate shrink and swell properties observed in subtropical soils from highland plateaus in southern Brazil, specifically in Oxisols with brown colors. In soils located in road cuts exposed to drying for some weeks, strong shrinkage of soil volume is observed in these soils, resulting in the formation of pronounced vertical cracks and large and very large prismatic [...]

Highlights

IntroductionShrinkage capacity (caráter retrátil in Portuguese), recently introduced in the Brazilian System of Soil Classification (SiBCS), is typical of some soils found in humid subtropical climate conditions of highland plateaus in southern Brazil, such as Oxisols with brown colors
Shrinkage capacity, recently introduced in the Brazilian System of Soil Classification (SiBCS), is typical of some soils found in humid subtropical climate conditions of highland plateaus in southern Brazil, such as Oxisols with brown colors
The most intense, wide, and asymmetric peak occurred at d values around 0.72 and 0.36 nm, positions typically attributed to 001 and 002 kaolinite basal planes (Brown et al, 1978; Barnhisel and Bertsch, 1989); this was seconded by less intense peaks, with d values of around 1.42 nm, usually indicating 2:1 expansive phyllosilicates or chlorite (Azevedo and Vidal-Torrado, 2009)

Summary

Introduction

Shrinkage capacity (caráter retrátil in Portuguese), recently introduced in the Brazilian System of Soil Classification (SiBCS), is typical of some soils found in humid subtropical climate conditions of highland plateaus in southern Brazil, such as Oxisols with brown colors In these soil classes, a marked shrinkage in the soil volume occurs after soil is exposed to drying conditions. The cation exchange capacity (CEC) of these soils is low, but when the values were converted to clay content, it is situated between 8 to 15 cmolc kg-1 in the B horizons Such values indicate low activity clays, but they are higher than many other purely kaolinitic or kaolinitic-oxidic Oxisols from other Brazilian regions. This medium to high CEC may be a contribution from the 2:1 HIV (hydroxyl-interlayered vermiculite) or HIS (hydroxyl-interlayered smectite) clay minerals and/or a contribution from interstratified kaolinite-smectite in association with kaolinite, as suggested in the literature (Melo et al, 2009; Teske et al, 2013; Yongue-Fouateu et al, 2016). Dudek and Środoń (2006) found CEC values higher than 100 cmolc kg-1 for pure smectite, and values between 25 and 100 cmolc kg-1 for kaolinite-smectite with less than 10 % of kaolinite layers in the interstratified minerals

Methods

Results

Conclusion