Clays and Clay Minerals, Vol. 56, No. 4, 429–436, 2008.
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Authors
Khademi, H.
Arocena, J. M.
Issue Date
2008
Type
Article
Language
Keywords
Periodicals , Geology , Kaolinite Neoformation , Palygorskite , Rhizosphere Effects , Sepiolite , X-ray Diffraction
Alternative Title
Kaolinite Formation From Palygorskite And Sepiolite In Rhizosphere Soils.
Abstract
Palygorskite and sepiolite are fibrous clays that occur mostly in agricultural soils of arid regions. Although many investigations have examined the environmental conditions for the formation and stability of these clays, informationonthe transformationof these clays inthe root zone (or rhizosphere) of agricultural crops is limited. Inthis study, changes inpalygors kite and sepiolite withinthe rhizosphere of selected agricultural crops were determined and the ability of plants to extract Mg from these minerals compared. Alfalfa, barley, and canola were cultivated in pots under controlled conditions in a growth chamber using growth media that consisted of a mixture of Ottawa sand and clay-sized Florida palygorskite (PFl-1) or Spanish sepiolite (SepSp-1). After 100 days of cultivation, the biomass of plant roots and shoots were determined and Mg uptake measured by inductively coupled plasma analysis of the plant biomass after microwave oven digestion. The clay fraction in each pot was separated from the sand and analyzed using X-ray diffraction (XRD) and examined using transmission electron microscopy (TEM). The XRD reflection at 0.718 nm clearly indicated kaolinite in the rhizosphere after growth of the three crops. Furthermore, hexagonal kaolinite particles were observed, using TEM, and the amount of Mg extracted by the three crops was significantly greater for sepiolite than for palygorskite. Palygorskite and sepiolite kaolinizationin the rhizosphere was apparently due: (1) to high acidity inthe rhizosphere caused by root activity and organic matter decomposition; and (2) to fibrous clay destabilization caused by Mg uptake by plants. This study shows that kaolinite in agricultural soils of arid and semi-arid regions might be partly due to neoformation after fibrous clay dissolution and not entirely inherited from parent materials, as has been suggested inearli er literature.
Description
Clays and Clay Minerals, Vol. 56, No. 4, 429–436, 2008. Kaolinite Formation From Palygorskite And Sepiolite In Rhizosphere Soils. H. Khademi; J. M. Arocena. DOI: 10.1346/CCMN.2008.0560404. Copyright © 2008, The Clay Minerals Society.
Citation
Clays and Clay Minerals, Vol. 56, No. 4, 429–436, 2008.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018, The Clay Minerals Society