Abstract
Major chemical forms of inorganic phosphate in Japanese farmland soils are phosphates sorbed by ac-tive Al and Fe under oxidizing conditions. Young volcanic ash soils and granitic soils contain apatite. The apatite re-acts with active Al in young volcanic ash soils after grad-ual formation of active Al. Dividing the Japanese farm-land soils into Andosols and lowland soils, phosphate is mainly sorbed by active Al in Andosols whereas by ac-tive Fe in lowland soils. A crystalline precipitate of phos-phate, vivianite, is formed under reducing conditions in the submerged lowland paddy field soils although Vivian-ite dissolves and the phosphate is sorbed by active Fe af-ter drainage. Other crystalline phosphates may be formed only under somewhat special conditions.
