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Morphology, Genesis, and Characteristics of Skeletal Soils in Sakon Nakhon Province, Northeast Thailand
Dissertation Abstract:
A study was conducted to characterize the morphological, physical, chemical, mineralogical, and micromorphological properties of the skeletal soils in Sakon Nakhon Province, Northeast Thailand. All the properties were used to identify soil forming factors that have influenced formation of the skeletal soils through the specific soil forming processes.
Eight representative pedons were selected for the detailed study based on their field morphology, parent materials, elevation, physiography, and vegetation. All studied soils were classified based on the US Comprehensive Soil Classitication System or Soil Taxonomy.
Morphological features of all the skeletal soils indicated the intermediate to mature stage of soil development with the A-Bt-C profile. All of them showed the discontinuity of soil materials within the soil profile. The skeletal layers (A and B horizon) of the transported materials were above the mottled clay or C hori zon, which was an in situ development from siltstone, shale, and mudstone. Soi ls with loose lateritic nodules were formed on the undulating terrains at high position, while soils with massive or sheet laterite were formed on the nearly-level to level terrains at low-lying position near the base level.
Kaolinite was an abundant clay mineral in most of the soils. particularly in the surface and subsoiI, except soiI on the Phu Ph an Range where illite was abundant. Montmorillonite, vermiculite, and ill ite were also present. Montmori lionite was abundant in the mottled clay and weathering horizon of some soils. Other minor and trace mineral were the interstratifted clay minerals between 10 and 14 A0, quartz, geothite, and gibbsite. Quartz was the most abundant mineral in the silt-size fraction, with traces of mica, feldspar, and 7 A0 group of clay minerals.
The micromorphological study also confirmed the discontinuity of soil materials. It indicated that il luviation was active in the subsoil, and shrinking and swell ing were active in the mottled clay horizon. Massive laterite was formed by the continuous cementing of various nodules by flow and layered ferruginous materials.
Two of the fi ve Alfisols were in the subgroup Ultic Haplustalfs, while the rest belonged to the subgroup Typic Ochraq ualfs. Aerie Ochraqualfs, and Aquultic Haplustalfs. The other three soi ls, including soil on the Phu Phan Range, belonged to the subgroup Plinthic Paleustults.