PHYSICAL AND CHEMICAL PROPERTIES AND CLAY MINERALOGY OF ANDOSOLS FROM KITAKAMI, JAPAN

Physical and chemical properties and the clay mineralogy of Normal and Light-Colored Andosols from Kitakami, Japan were studied. The profiles of both Andosols had features reflecting the repeated falls of tephras with different ages. The Normal Andosol, which is a common Andosol in Japan, showed unique properties, such as large total porosity, high water retention, low bulk density, remarkable accumulation of organic matter, high fluoride pH value, large phosphate absorption, etc. The Light-Colored Andosol, which was formed by truncation, also had some of these unique properties. It was noted that chloritized 2:1 minerals were dominant, and allophane and imogolite were absent in the clay fractions of all the soil samples derived from volcanic ash, whereas allophane and imogolite were dominant in the clay fractions of all the soil samples from pumice. It had been assumed that the unique physical and chemical properties of a common Andosol were largely attributable to the high content of allophane. The results obtained in this study show, however, that most of the unique properties of the Andosols from Kitakami are closely related to the dithionite-citrate-soluble constituents, especially alumina, to a great extent.