For amorphous matters of humic soils the author proposes a model representing a complex of mutually combining active elements, that is, humus, amorphous sesquioxides, allophane and layer silicate clays. It is shown that apparent and net activities of allophane and humus can be quantitatively differentiated according to the model. Humic soils are classified into five types, I, IIa, IIb, IIc and IId, as regards negative and positive activities of allophane, assumed from i-charges, o-charges and phosphorous adsorptions of both original and hydrogen peroxide treated samples. Type I is a group of humic soils, the poorest in allophane, to which belong problematical "Kurobobu" soils of Tokai district and volcanic ash soils such as at San'in and Hokuriku districts. Types IIc and IId comprise one, the richest in allophane, to which belong most of humic soils near volcanoes having been in activity through Holocene. Types IIa and IIb are intermediate between both of the above. X-ray diffraction and DTA of clays for each type well confirm the allophane content assumed from the model.
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