Abstract
The estimation methods of water holding capacities and material retention capacities of the soils, and the mapping methods of soil groupings and water conservation capacities were studied in a small watershed. The water conservation capacities of the soils in the Hosaki small watershed were also estimated. 1) For the Hosaki River small watershed, a 1/5,000 large-scale soil map divided into 45 soil groupings was produced. 2) The map was digitized with a 10 m grid, and the distribution area of every soil grouping was estimated. By multiplying the water conservation capacity by the distribution area of the soil grouping, the water conservation capacity of every soil grouping in the small watershed was estimated. 3) The whole soil volume in 288.9 ha of the small watershed was 6,399,785 m^3, the maximum water retention capacity 3,976,696 m^3, the 0-5 kPa water retention capacity 983,867 m^3, and the 5-50 kPa water retention capacity 446,303 m^3. In addition, the small watershed had PAC of 5,685 Mg, AEC of 118,192 kmol(-), and CEC of 852,587 kmol(+). 4) Though the water holding capacities of the soils were the biggest in the mountain and comparatively big even in the upland, they were small in the lowland. 5) Though the material retention capacities of the soils were the biggest in the upland and comparatively big even in the mountain, they were small in the lowland.
