The so-called “Kanto Han-shitsuden” occupy a considerable percentage of the total paddy field area in Kantö District (Japan). “Han-shitsuden” means semi-swampy field, where “gley layer” and the ground water table (in winter) stay at 60-80cm below the soil surface. We have carried ont field researches of physical properties (especially permeability) of some of their soil protiles through a year round. The results are reported in this paper.
1. In the two research fields situated at Soshigaya and Katsushika, both in the suburbs of Tokyo, it was found that the profile contained a hard pan at about 20cm below the surface, the material of which was of higher bulk density and of lower porosity than in subsoil layers. A remarkable accumulation of iron oxide and manganese oxide was observed beneath the hard pan.
2. A plenty of large pores, such as cracks or fissures filled with decayed roots of marsh-reed, were found in the horizon under the furrow slice. Owing to these pores, the permeability of soil samples revealed local fluctuations remarkably.
3. Under the flooded condition, the water pressure head in each level of the profile was never negative, but was positive and in “closed” condition. Therefore it can be stated that in the soil profile there existed neither free water surface nor “pseudofree water surface” in the flooded condition.
4. In the oxydation and reduction measurements, it was observed that the furrow slice layer was in reductive and oxidative conditions in irrigation and non-irrigation respectively, the “gley layer” was in reductive condition all through the year, and the inter-layer was in oxidative condition even in irrigation season.
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