Iron oxides dynamics in a subtropical Brazilian Paleudult under long-term no-tillage management

Alberto Vasconcellos Inda,Vidal Barrón,Cimélio Bayer,José Torrent,Jessé Rodrigo Fink

doi:10.1590/s0103-90162013000100008

Alberto Vasconcellos Inda, Vidal Barrón + Show 3 more

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https://doi.org/10.1590/s0103-90162013000100008

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Abstract

Replacing conventional tillage (CT) with no-tillage (NT) management alters the pedoenvironment and the rate of topsoil processes, with possible effects on dissolution processes associated with iron oxides and therefore soil mineralogy. This study aimed to determine the effect of NT on the content and distribution of types of iron oxides in a Rhodic Paleudult in southern Brazil. Soil samples were collected at eight depths within the 0.00-0.80 m layer under CT and NT in a long-term experiment (21 years). Mineralogical identification was conducted by X-ray diffraction (XRD), and the Fe content related to specific types of iron oxides determined by selective dissolution and diffuse-reflectance spectroscopy. Kaolinite, quartz, goethite, hematite, and maghemite were identified in the clay fraction. In the NT-managed soil, there was a decrease in the content of crystalline iron oxides and an increase in the content of poorly crystalline iron oxides with increasing proximity to the soil surface. These results suggest that iron oxides are rearranged in this soil by reductive dissolution of the crystalline types and neoformation of metastable ferrihydrite in topsoil layers, which should be assessed further in laboratory studies.

Highlights

Iron (Fe) oxides influence the physical and chemical behavior of tropical and subtropical soils (Bigham et al, 2002; Cornell and Schwertmann, 2003)
Mineralogical identification was conducted by X-ray diffraction (XRD), and the Fe content related to specific types of iron oxides determined by selective dissolution and diffuse-reflectance spectroscopy
These results suggest that iron oxides are rearranged in this soil by reductive dissolution of the crystalline types and neoformation of metastable ferrihydrite in topsoil layers, which should be assessed further in laboratory studies

Summary

Introduction

Iron (Fe) oxides (here including oxides, hydroxides and oxyhydroxides) influence the physical and chemical behavior of tropical and subtropical soils (Bigham et al, 2002; Cornell and Schwertmann, 2003). Considering recent changes in the soil environment, Silva Neto et al (2008) proposed to investigate the effect of notillage (NT) on the dynamics of Fe oxides in soils previously under conventional tillage (CT) management This new condition, characterized by an increased organic matter content and lability, moisture content, and microbial activity, favors reduction and complexation, which are the main dissolution reactions for iron oxides in pedogenic environments (Schwertmann, 1991). This hypothesis was tested by Silva Neto et al (2008) in an Oxisol cultivated for 18 years under NT management, and the authors observed alterations in distribution of the total content of pedogenic Fe oxides and the mineral forms with low crystallinity. The Fe levels of types of Fe oxides were not discriminated, the authors suggested that the new conditions in the NT-managed topsoil layer promoted reductive dissolution of some crystalline types (hematite and maghemite) and neoformation of metastable types of low crystallinity (ferrihydrite)

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