Distribution of allophanic andosols and non-allophanic andosols in Japan
1998
Saigusa, M. (Tohoku Univ., Sendai (Japan). Faculty of Agriculture) | Matsuyama, N.
Andosols occurring in Japan are divided into allophanic Andosols and non-allophanic Andosols. In contrast to allophanic Andosols, non-allophanic ones have clay fraction dominated by 2:1 minerals and mostly contain large amounts of KCl-exchangeable Al. Consequently, crop production on non-allophanic Andosols are often severally restricted by Al toxicity. Therefore, distribution and formation of both allophanic Andosols and non-allophanic Andosols in Japan were studied. The distribution patterns of those Andosols were closely related to the thickness of deposit of Holocene tephra or/and Late Pleitocene one rather than climatic condition such as amounts of precipitation and precipitation effectiveness (P-E) index reported by other researchers. Namely allophanic Andosols were mainly distributed in the areas having thick depositions of Holocene and/or Late Pleistocene tephras and occupied 4.51 million ha or 69.9% of total land areas of Andosols in Japan. On the other hand, non-allophanic Andosols were scattered in the area having poor deposition of these tephras and occupied 1.95 million ha, or 30.1% of total Andosol. Compared to allophanic Andosols, non-allophanic ones showed thicker high humus horizon but smaller amounts of active Al suggesting the occurrence of dilution of humus horizon by the contamination of exogenous materials such as loess from china
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