As a result of the investigation of relationship between cation exchange capacity and the soil texture by the method of Intenational Society of Soil Science in two kinds of igneous rock soils, these soils were estimated to be the uncommon soils, in which cation exchange capacities of larger particles than clay were considerably high. In order to clarify this estimation, cation exchange capacities of the different sized-fractions separated from upper layer soils and lower layer ones were studied. The results were as follows :
1) Cation exchange capacities of clay sized-fractions were about 30 me. in No.1 soil and 40 - 63 me. in No.2 soil. Those of larger different sized-fractions were about 25 me. in No.1 soil and 15 - 25 me. in No.2 soil.
2) In No.1 soil, the ratio of cation exchange capacity of clay sized-fraction to total one was 41 % in upper layer and 17 % in lower layer. In No.2 soil, it was 50 % in upper layer and 12 % in lower layer.
3) In all soils, the total amounts of cation exchange capacitles of the different sized-fractions were higher than cation exchange capacities of original soils.
The changes of cation exchange capacities of fine sand sized-fractions by shaking in <Na>_2CO_3 and NaPO_3 solution were studied. The results were as follows :
1) By shaking in <Na>_2CO_3 solution, cation exchange capacities were increased in No.1 soil and did not, in No.2 soil.
2) By shaking in NaPO_3 solution, those were increased in No.1 soil and did not, in No.2 soil.