排水条件を異にする黒ボク土の粘土鉱物組成

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For characterization of Andosols, formations of clay minerals were studied on two profiles of Andosols. The two adjacent soils are on a terrace in Tsukuba, and different each other in microrelief, soil moisture regime and humus contents. One is a Humic Andosol (corresponding to Typic Dystrandept, medial over loamy, mixed, mesic of U. S. Soil Taxonomy), located on relatively high elevation. The other is a Thick High- humic Wet Andosol (Aquic Dystrochrept, medial over loamy, mixed, mesic), located on depression of the terrace. The difference in elevation is about 1 m between the two sites. Mineralogy and some chemical and physical characteristics samples from the two profiles were investigated. Amorphous constituents such as allophane and imogolite are dominant in the clay fractions of all horizons of the Humic Andosol and upper horizons of the Wet Andosol. Halloysite (10 A) is dominant in clay fractions of lower horizons of the Wet Andosol. The difference of clay minerals may be attributed to the soil moisture regimes. In well-drained Andosols on relatively higher elevations, concentration and precipitation rates of silica and alumina may exceed crystalization rate from silica and alumina to layer silicates, which, consequently, may cause amorphous clay formation. On the other hand, stagnant water in soils of the depressions may support crystallization of halloysite. The aquic moisture regime retards oxidation of organic matter. The accumulated humus may fix aluminum. This might make the concentration of silicon relatively high and contribute to the formation of halloysite.[figure]

排水条件を異にする黒ボク土の粘土鉱物組成

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