Pedogenetic Studies on Some Selected Soils in Northeast Thailand : I. General Soil Characteristics

Abstract The properties of the major five upland and five paddy soils distributed on the plateau of Northeast Thailand, which were characterized by a sandy surface overlying the loamy to clayey substratum, were investigated. Mass movement such as creeping on the slope was considered to have played an Important role in the formation of the parent materials. During the mass movement, clay particles, mainly smectite, were selectively transported and accumulated at the foot, leaving the more sandy parent materials in the upper part of the plateau and resulting in the more clayey parent materials in the lower part. Among the upland soils, the amount of smectite appeared to be slightly larger in the soils at the summit than in the soils in the middle slope, presumably due to the mass movement, Indicating the importance of this phenomenon. The large amount of exchangeable Na was conspicuous In the paddy soils which were considered to be non salt-affected, Indicating the expansion of salinization. In the low-lyin...