Soils of the left-bank area along the Ado River, Shiga Pref., were surveyed and mapped on 1:10,000 scale to give an information on basic natural conditions for landscape planning in rural areas. In the survey, the author applied the several soil units so far used in Japan, but modified them in somewhat a different way to conform them to the complicated geomorphological setting. The surveyed area comprises the Ado River delta, Plio-Pleistocene hills which retain the flat surface capped by red-colored soils, the dissected steep hillslope, and the river terraces. Soils on hills have, except on the steep hillslope, the "polygenetic" profiles as exhibited by the so-called buried Kuroboku soil. Although the origin of the Kuroboku may be controversial, it is without doubt that the mass-wasting or erosion-deposition process of soil material contributes considerably to the formation of the above-mentioned soil profiles. This process is also presumed to be in action in soil profiles apparently monogenetia, because the formers very often fade away into the latters. These observations made the author to presume a hypothesis on the stratigraphic superposition of soil horizons, which are influenced also by the "soil formation processes." The distribution of thus formed soil profiles show the regularity in accordance with the topo-, litho-seqence of the terrain. Therefore, the author was led to conceive the morphological soil units, which are not very strictly genetic, but might be effective aud mappable in showing the characteristics and extension of soils. To be applicable for a wide range of the scale of maps, multicategorical arrangement of soil units was aimed; soil type, subtype, genus, soil variety, sub-variety as major categories, and form and phase as sub-categories. Soil type, in the use of some europan, russian schools and some japanese scientists, was employed as a fundamental category, which covered the following: Red-yellow soil, Brown forest soil, Ranker, Pseudogley, Brown lowland soil, Gray-brown lowland soil, Gray lowlond soil, Gley lowland soil, Anmoorgley, Moorgley, and Regosol. The second important category is soil varieties, which subdivides the soil units in higher categories based on the development of profile intrinsic to each soil type. The criteria are: humus type, soil structure, horizon boundary etc., which reflect the water regime in case of Brown forest soil (Forest Soil Division, 1975), Red-yellow soil, and Ranker; the occurrence of stagnant water whether due to the impermeable layers or to topograhic occlusion in case of Pseudogley; the degree of the inner drainage of soil in case of lowland soil types; and the occurrence of moor or anmoor horizon whether appearing from the surface or covered by mineral horizons in case of Moorgley and Anmoorgley. Soil varieties were subdivided into sub-variety based on the solum thickness, and/or development of paddy soil profile, and/or intervening horizons specific to other soil types. In the category of form were described the geomorphological position, and/or parent material, and/or texture. Microtopography and gravel or gravelly layer were described in the category of phase. Subvarieties combined with form and phase were used as mapping units, as well as soil association and complex of them, when necessary, in accordance with the soil survey manual (USDA, 1951). The use of airphotos was very effective in delineating the soil type boundary. Some features useful for the physiographic mapping (Beckett, 1968) in the area were discussed.
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