In this paper, amounts and compositions of humus in the volcanic ash soils are considered in relation to the bioclimatic conditions in Japan. (1) According to various reports of soil survey on arable land, the abundant accumulation of humus are found in uplands of Japan-Sea side of Honshu, northern Kwanto, and southern Kyushu, as well as hilly lands of northern Kwanto, San in, and central Honshu. (2) The humus compositions of the volcanic ash soils, representative of these districts are examined after PONOMAREVA'S method. The results obtained are as follows: the ratios of humic acids to fulvic acids lie from 0.4 to 1.8, and the most part of humus is composed of fraction-1, -la, and 4. The differences among the respective soils are indicated by the ratio of humic acids to fulvic acids and the distribution patterns of fraction-1, -la, and -4 in the soil profiles. (3) The humus compositions of soils in the hilly lands of central Honshu are analogus to those of the Brown forest soils examined by TYURIN. In the uplands of Kwanto and northern Kyushu those are analogus to the Red soils examined by SABASHVILL While those in Japan sea side of Honshu have the intermediate character between those of the Brown forest soils and Red soils. (4) From the abovementioned results, it may be assumed that the most of volcanic ash soils in Honshu and Kyushu are identified with the Humified Allaphanic soils proposed dy GERASSIMOV.
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