Soil and landform features of mountainous terrain in South Thailand

The results of reconnaissance surveys over 2,000 Km² are used to described mountainous terrain on granite, gneiss and pelite. Detailed morphological and laboratory analytical data are presented for soils derived from each of these rock types. The soils, which are classed as Paleudults, are acid, kaolinite-rich and deficient in nutrients. Soils formed on granite and gneiss have high proportions of coarse quartz particles (2.0–50.0 mm); the dilution effect of this inert material further reduces their effective nutrient status. The degree of weathering, as indicated by the silt:silt+clay ratio, increases with profile depth.Mean gradients recorded on the granite and pelite hillslopes are 27° and 29°, respectively. A greater uniformity of slopes was observed on pelites than on granites; the ‘missing angle’ technique was employed to identify ‘natural’ slope classes. Gradients tend to increase downlopw, indicating a rapid removal of erosion products at the footslope and a rejuvenation of the valleys. A significant association was recorded between soil depth and slope gradient on pelite but not on granite or gneiss landforms.