Extremely acid lowland soils have been known, in general, as acid sulfate soils. Many studies have been conducted on these soils in the Lower Central Plain where their extensive area exists." However, these soils can also be found along the Southeast Coast and in the coastal areas of Peninsular Thailand in association with Organic Soils (Histosols)" where accumulation of organic materials in the soils is uncommonly excessive." Some of these ex- tremely acid lowland soils appeared to have recently passed through a stage of being Organic Soils before developing further, due to drainage and oxidation, to become mineral acid sulfate soils." Therefore, one can expect to see some layers of the organic materials preserved in the profiles of acid sulfate soils in these two areas (Southeast Coast and Peninsular Thailand). A similar situation was reported also for some acid sulfate soil profiles in the Central Plain.3 Under a tropical monsoonal grading towards tropical rain forest climatic regime', acid sulfate soils in the Southeast Coast and Peninsular Thailand can be expected to develop faster than the ones in the Central Plain due to a higher and better distribution of rainfall. This should have some bearing on their characteristics and utilization.
