Clay minerals and humus complexes in five Kenyan soils derived from volcanic ash |
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| Affiliation: | 1. Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK;2. Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, UK;3. School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP, UK;1. Department of Mining and Nuclear Engineering, Missouri University of Science and Technology, Rolla, MO 65409-0450, USA;2. University of Kentucky, Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, USA;3. Pattison Sand Company, Clayton, IA 52049, USA;1. Institute of Physics, University of Tartu, W. Ostwaldi 1, 50412 Tartu, Estonia;2. Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga, Latvia;3. RMS Foundation, Bischmattstrasse 12, Bettlach 2544, Switzerland;4. Institute of Geological Sciences, University of Bern, Baltzerstrasse 1–3, Bern 3012, Switzerland;1. Department of Engineering Geology, Institute of Rock Structure & Mechanics, The Czech Academy of Sciences, V Holešovičkách 41, Prague 182 09, Czech Republic;2. Czech Geological Survey, Brno Branch, Leitnerova 22, Brno 658 69, Czech Republic |
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| Abstract: | Clay minerals and humus complexes and their effects on soil chemical properties were studied for five profiles around the Longonot and Susua volcanoes in Kenya. Morphologically, all profiles have some resemblance to Andepts, but there were clear-cut differences in clay contents and mineral composition as well as pH between profiles 1 through 4 and profile 5, which occur under semi-arid to subhumid and under humid climatic conditions, respectively. Profiles 1 through 4 contained embryonic halloysites with X-rays amorphous iron oxide and silica, whereas profile 5 contained a kaolin mineral, chloritized 2:1 layer silicates, gibbsite and hematite. These mineral associations probably represent early and advanced stages of weathering of volcanic ash under weak and strong leaching conditions, respectively. Embryonic halloysites consisted of more or less poorly ordered halloysite and “1.0- and 0.7-1.0-nm minerals”. The carbon contents of A horizons ranged from 100 to 112 g/kg in profiles 2, 3 and 5. Humus complexes increased in the order; Fehumus ⩽ Al-humus ⩽ Ca-humus in profiles 2 and 3, whereas Al- and Fe-humus were found exclusively in profile 5. The pH (NaF), phosphate retention and acid oxalate extractable Al qualify only profile 5 as an Andept or Andisol. |
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