Soil Physicochemical Properties and Geochemical Indices: Diagnostic Tools for Evaluating Pedogenesis in Tephra-Derived S
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OIL CHEMISTRY
Soil Physicochemical Properties and Geochemical Indices: Diagnostic Tools for Evaluating Pedogenesis in Tephra-Derived Soils along the Cameroon Volcanic Line R. K. Enanga, *, B. P. K. Yerimaa, G. K. Komea, and E. Van Ranstb aSoil
Science Department, Faculty of Agronomy and Agricultural Sciences, University of Dschang, Dschang, P.O. Box 67, Cameroon b Department of Geology, Faculty of Sciences, Ghent University, Ghent, 9000 Belgium *e-mail: [email protected] Received November 1, 2019; revised March 6, 2020; accepted March 27, 2020
Abstract—Physical and geochemical properties of six soils developed on tephra from Mts. Kupe and Manengouba were studied in order to assess the degree of weathering of the tephric parent materials. Physico-chemical properties were determined following standard procedures. Total elemental contents and selective extracted contents of Al and Fe by acid ammonium oxalate, dithionite-citrate-bicarbonate (DCB) and pyrophosphate were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) after being brought into solution. Parent rocks were chemically classified as hawaiite, tephricfoidite, and basanites, while soils were classified as Andosols and Cambisols. Both the soils and parent rocks have high concentrations in SiO2, Al2O3, and Fe2O3. Texture and the evaluated related weathering indices correlate with horizon development and are important in capturing the differences between the two Reference Soil Groups. Mobility of major elements showed erratic trends in conformity with the stratigraphic breaks indicating variability of parent materials with depth. Enrichment and depletion of major elements to a certain degree explains the ongoing andosolization process in the Andosols. Physical and geochemical data can both be used concomitantly for assessment of weathering trends in these soils. Total reserve in bases (TRB) is very high in the Andosols indicating the presence of large quantities of weatherable minerals and thus the high potential of these soils for agricultural production. Keywords: Andosols, Andosolization, Cambisols, element mobility, Mt. Kupe, Mt. Manengouba, weathering indices DOI: 10.1134/S1064229320080050
INTRODUCTION The concentrations of major elements and the amounts of volatiles (notably H2O+ and H2O–) are very important in the determination of various weathering indices both in rocks and soils [33]. They are used to assess the degree of soil weathering, pedological variability and extent of profile development [5]. They proved useful guide to the physical, chemical, and engineering properties of weathered rocks [34], and they are used for the prediction of parent materials from which soils have developed [47], and for the estimation of the degree of mineral weathering [13]. The relationship between chemical composition of a soil and that of the parent rock is generally assessed using concentrations of major elements, while the degree of weathering is generally assessed using various weathering indices such as: the Ruxton ratio [34]
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