In order to clarify the index of a maturation of plow layer soil of drained area by the method of civil engineering, the change of soil structure(ped and void of soil) caused by grass culture was investigated in YASUGI region of NAKAUMI drained area.
The results obtained are as follows :
1) The change of structure of soil ped by grass culture is showed in the subdivision of ped structure, namely, coarse peds(25-10mm) are reduced and fine peds(under 5mm) increase as compared with the soil left as it is.
2) The change of structure of void is showed in the reduction of the gross volume of void, namely, coarse void(pF1.8-0) decreases and fine one(above pF4.0) increases.
3) These tendency are recognized more conspicuously in fine(clayey) soil.