Abstract
Groundwater aquic soils and anthraquic soils coexist in Gray Lowland soils, and are not separated in the classification system of cultivated soils. But the difference is important from the viewpoint of water dynamics, soil management, and land use. Shapes of mottles seem diagnostic in separating the two types, i. e., cloud-like iron mottles and spotty manganese mottles are characteristic of anthraquic type, while tube-like iron mottles are characteristics of aquic type. Using the data base of Soil Information System (JAPSIS), an attempt was made to separate about 5,000 profiles of soils between aquic and anthraquic types, based on the shapes of mottles. Separation seems fairly satisfactory because the two types of soils show consistent difference in other soil properties, e. g., hardness, structure, etc. The regional distribution of these two types was also evident: groundwater aquic type dominates in Northeast Japan, and anthraquic type is widespread in Southwest Japan. The mechanism which gave rise to this regional specificity was discussed in terms of the forming process of anthraquic Gray Lowland soils.
