With reference to the amount of amorphous materials of the selected soils, it is summarized that Andosols (Kuroboku soils) in Japan may be divided into three groups: 1) soils that have the amount of amorphous material of more than 20% on the oven-dry basis, and more than 50% in the clay fraction, deriving from wind-blown volcanic ash, 2) soil that have more than 10% on the oven-dry basis, and more than 20% in the clay fraction, deriving from ash influenced or redeposited and/or from wind-blown volcanic ash with well developed soil profile, and 3) soils that have less than 5% on the oven-dry basis, but more than 85% in the clay fraction, deriving from young coarse textured volcanic material.
　Phosphorus absorption coefficients ranged from 15.00 (3440) to 9.90 (2270) P mg/g (P₂O₅ mg /100 g) except for young coarse textured horizons, and it seems not directly related to the amount of amorphous material.