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Botswana International University of Science & Technology (BIUST) 2022

Mineral weathering, pedogenesis and characterization of expansive soils from Serowe, Central Botswana

Nkonga, Itumeleng

Titre : Mineral weathering, pedogenesis and characterization of expansive soils from Serowe, Central Botswana

Auteur : Nkonga, Itumeleng.

Université de soutenance : Botswana International University of Science & Technology (BIUST)

Grade Msc Environmental Science 2022

Résumé partiel
Expansive soils tend to be fairly high in natural fertility and their unique morphology makes them quite interesting. Soils found in Serowe, Central Botswana, commonly exhibit variable degrees of periodic shrinking and swelling which often leave visible cracks and sometimes undulating micro-topography (gilgai) on the landscape. The use of expansive soils is often constrained due to severe management problems often associated with their physico-chemical properties. Therefore, basic site-specific pedological research is pivotal to understanding some of the unresolved edaphological and environmental aspects of expansive soils. The overarching aim of this study is to undertake a pedological investigation of the expansive soils from Serowe, which hitherto have been poorly studied. The main objective of this study is to advance our understanding on the pedology of the soils from Serowe. Specific objectives include to : (i) characterize the soils using macromorphological, physical, chemical, mechanical and mineralogical properties ; (ii) evaluate mineral weathering intensities of the soils ; (iii) identify the pedogenic processes responsible for their formation ; and (iv) provide an updated high resolution classification of the soils in accordance to FAO-WRB system and USDA Soil Taxonomy. Five representative soil profiles (SP1, SP2, SP3, SP4 and SP5) were randomly sited on flat to undulating landscapes and samples were collected from each genetic horizon for laboratory analysis. Selected pedological parameters including particle size distribution, pH (H2O and KCl), bulk density, porosity, organic matter, calcium carbonates contents, electrical conductivity, cation exchange capacity, coefficient of linear extensibility (COLE) and Atterberg limits were determined using routine laboratory procedures. X-ray fluorescence spectrophotometer and x-ray diffractometer were used for total elemental composition and clay mineral analysis respectively. Geochemical ratios including CIA, CIW, and ICV were used to assess mineral weathering ; mass-balance plots for elemental redistribution and pedogenic ratios for quantitative pedogenesis

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