Abstract: Characteristics of sulfur forms, content, distribution and its acidification of Acid Sulfate Soils (ASS) in the southern coastal regions of Taishan city, Guangdong, are studied. The results show that the sulfur content of ASSis very high, 2 to 6 times than coastal saline soil, 3 to 9 times than paddy soil. The sulfate of ASSis mainly in inorganic forms, it covers 82.3% to 90.4% of the total sulfur in the soil. Among them, pyrite is the highest form; it covers 30.3% to 46.2% of the total sulfur in the soil. The distribution of pyrite in profile is corresponding with the total sulfur. The difference of sulfur content in the profile and between the soils is significant. The sulfur is very high in the place where near the hill. This means the suitable sulfur accumulation place is near the hill. Acidity of ASS is come from pyrite oxidation. The acidification cause pHvalue drops to 5.5, even to 2.83. The potential acidity of ASS is 2 to 3 time high than the actual acidity, the potential environmental risk of ASSis great.

Key words: Acid sulfate soils, Sulfur, Acidification characteristics, maize-soybean relay intercropping, P use efficiency, adsorption-desorption., P application rate, P application depth