Abstract
In this investigation, the particle size distribution of Akahoya soil was determined to understand the relationship between the degree of weathering and depth from the land surface of Akahoya soil. Akahoya soil can be divided into three types of group mainly based on the depth from the land surface. Type I, Type II, and Type III are buried at less than 150 cm, about 200-400 cm and 300-700 cm from the land surface, respectively. Akahoya soils are dominant in fine sand particles, the contents of which change in relatively wide range among Akahoya samples. Correlation between the clay and fine sand contents (%) of Akahoya soils showed close negative relationship. It is important to point out that clay particles originated from fine sand particles, as a result of weathering of these particles. Coarse sand contents of Akahoya soils abrubtly increase with decreasing distance from its origin and retain main characteristics of tephra fall. On the other hand, the silt contents of Akahoya soils exhibited the least change in the proportion which ranges from 17.3-28.6% compared with the other soil particles. Moreover, parent materials (Akahoya tephra (f_3)) of Akahoya soils were estimated to contain 70-75% fine sand. The clay contents are useful in estimating the degree of weathering of the three types of Akahoya soils and that the rate of weathering is in the order of Type I>Type II>Type III. This fact suggests that weathering of tephra fall progresses more rapidly on the land surface than in the underground.
