Abstract
In order to elucidate the genesis of the so-called "non-volcanic" kuroboku soil in the Tokai district, Japan, forest soils in the north-eastern part of Aichi prefecture were analyzed on the content and the refractive index of volcanic glass as well as the chemical properties related to the volcanic origin. The samples included 3 acid brown forest soils as well as 4 koroboku soils. (1) All of the soils contained more or less volcanic glasses. According to their refractive indices, the volcanic glasses were inferred as originating from Aira-Tn and/or Akahoya ashes. (2) The carbon contents of the A horizons were 6〜19% and did not differ between the kuroboku and the brown forest soils. The C to N ratios of A horizons, however, were larger than 20 in the kuroboku soils and less than 20 the brown forest soils. (3) All the samples were strongly acidic, that is, pH (H_2O)≤5.0, pH (KCl)&;e;4.1 and the exchange acidity Vj ranging from 9 to 65. (4) Phosphate absorption coefficients were 1300〜1900 in the kuroboku soils, and on the other hand 7 out of 14 brown forest soils samples had the value more than 1300. (5) Exept for one brown forest soil profile, all the soil profiles contained one or more horizons of pH(NaF)≥9.4. (6) Allophane test using KF solution and phenolphtalein paper showed the clearly positive reaction on 2 kuroboku and 2 brown forest soils. (7) Humic acids of A type were recognized in the A horizons of all the kuroboku soils as well as in a buried humic horizon and a B horizon of the brown forest soils. (8) Based on the results obtained above, it was considered that, the kuroboku soils developed at first after the falls of wide-spread ashes and then they were eroded, subsequently the brown forestsoils were formed, though some parts were protected from erosion and reworked areas remained as kuroboku soils.
