Abstract
Distributions of allophanic Andosols and nonallophanic Andosols in Western Japan (Kinki, Chugoku, Shikoku and Kyushu Districts) were determined. 376soi1 samples were divided into two groups according to the ratio of pyrophosphate extractable Al/acid oxalate extractable Al, the amonts of acid oxalate extractable Si and the clay contents: allophanic Andosols and nonallophanic Ando-sols. Allophanic Andosols were mainly distributed in central and southern parts of Kyushu District having thick depositions of Holocene tephra and occupied 889,000 ha, or 64%of total Andosols. On the other hand, nonallophanic Andosols were scattered in the regions having poor depositions of Holocene tephra such as Kinki District, Chugoku District, Sikoku District and northern part of Kyushu Districts and occupied 508,000 ha or 36% of it. The distribution patterns of allophanic and nonallophanic Andosols were closely related to the thickness of Holocene tephra deposition rather than climatic condition such as precipitation and P-E index: thick deposition of Holocene tephra for allophanic Andosols and poor deposition of it for nonallophanic Andosols.
