Factors relating to labile phosphate levels in volcanic ash soils

The low availability of phosphatic fertilizer owing to the fixation of phosphorus in acidic volcanic ash soils has been noticed by many soil scientists in Japan. However, in spite of the early recognition, few studies have recently been made to obtain fundamental information on the phenomenon. It has been thought that a large amount of dressed phosphates are precipitated by soluble cations, especially by aluminum ion, or physicochemically sorbed hy the absorbing complex of volcanic ash soils where allophane and sesqui-hydroxides play major roles in the phosphorus fixation.