Several studies of acid sulfate soils in coastal lowlands have been conducted; however, little attention has been paid to the correlation between the properties of acid sulfate soils and their associated soils. This research aims to study soil properties and their influences on acid sulfate soil development as well as the pedogenesis process of acid sulfate soils. The morphological, physical, chemical and mineralogical properties of acid sulfate soils and their associated soils in the Lower Central Plain of Thailand were determined. According to the different profile forms of all soils, the results were assigned to one of four profile types (A-D). The results reveal that pyrite was accumulated in the lower parts of soils of all profile types. Most of the soils had high organic carbon levels in their subsoil and were associated with pyrite accumulation. Alkaline ions effected acid sulfate soil development and jarosite appearance. Ca was the most important alkaline cation that reacted with acidity. Most types A, B and D profile soils had high acidity but low alkalinity. These soils developed into acid sulfate soils. Type C profile soils contained excess Ca, so they developed into non-acid sulfate soil. The strong acid conditions type A, B and D profile soils efficiently elevated kaolinite formation. In contrast, the alkaline conditions of type C profile soils elevated smectite formation. Pyrite had a strong correlation with total S and consequently, the amount of pyrite in each profile type could be estimated from the total amount S in the soils.
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