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A study on characteristics and fertility capability of acid sulfate soils under tropical monsoonal climate was carried out on six selected areas in Nakhon Si Thammarat province. Method of study included analysis of soil morphology in the field, laboratory analysis on physicochemical properties and mineralogical characteristics of soil samples according to standard methods and assessment of the soil fertility status and fertility capability. Results of the study revealed that these soils are lowland soils occupying areas ranging from 1 to 5 m above mean sea level. These soils developed on brackish and marine deposits, and organic materials. They are deep to very deep and poorly developed. These soils are ultra acidic to moderately alkaline (pH 3.1-8.3) and their organic matter content varies from very low to very high (0.3-356.9 g/kg). They have low to very high cation exchange capacity (9.0-80.0 cmol/kg) and low to high base saturation percentage (7.9-92.8 percent) The soils have kaolinite as the major mineral in clay fraction. These soils include three areas of Sulfaquepts and three areas of Endoaquepts. They have low to medium fertility and their limitation for agricultural use comprises acidity associated with jarosite, gleying, mostly deficient available potassium and with aluminum toxicity in some areas. The main agricultural soil management practices include controlling of water table levels, liming for most soils, proper crop type selection and plant nutrient management emphasizing potassium to improve their fertility.
