Author : Sunan Kunaporn

Summary : A study on characteristics and genesis of soils in eco-floristic zone was conducted at Doi Inthanon National Park, Chiangmai Province. Ten soil profiles in this area were selected for a detailed study on field morphology. Their physical and chemical properties, mineral compositions, and micromorphology were determined using PEDONS as sampling sites. Results revealed that these soils were developed from residuum and colluvium of granite and gneissic granite rocks. All ten soils had deep to very deep profiles and were well drained. The texture of profiles varied from sandy loam to clay with black to very dark grayish brown to red color. The percentage of water retention was moderately high to high and bulk density was moderately low. Clay coating materials were distinct in a form of ferri-argillan, characterizing an argellic horizon in all B horizons except profiles D1-1, D1-2, and D1-3. Profile D1-2, particularly, had formed a spodic horizon. Kaolinite was the dominant clay species in all profiles, except profiles D1-2, D1-5 and D1-10 which were dominantly gibbsite. Quartz was the major primary mineral species with minor compositions of muscovite, chert, tourmaline, gibbsite, and feldspar. The soils had minor amounts of non-resistant weatherable minerals and were very strongly acid to moderately acid in reaction. The organic carbon content and cation exchange capacities (CEC) of these soils were high at the surface and low in the subsoil. The base saturation of soils at low altitudes was more than that of the soils at high altitudes. The available phosphorous and potassium at the surface was higher than in the subsoil. The free iron oxide varied throughout the profiles. The ten soil profiles were classified into four orders. The alfisol soils were profiles D1-6 to D1-9. The ultisol soils were profiles D1-4, DI-4, and D1-10. The inceptisol soils were D1-1 and D1-3. Profile D1-2 was classified as spodosols.