Following the our previous report, this time also, 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 followes :
1) In the case of continuation of grass culture, namely case A, soil peds were restructured and coarse peds(l0mm or more) increased. On the other hand, in case of soil left as it is, case B, it was progressing to break a clod into fine pineces.
2) The above mentioned tendency was more obvious in the case of wet seave method, i. e., water resistance aggregates were formed in case A, otherwize, in case B, a clod was broken to fine grains of diameter less than 1mm.
3) In case of A, a clod was very stable to slaking and crumbled scarcely in water, but in case of B, a clod broke down easily.
4) By grass culture, coarce pores (corresponding pF 1.8 or less) decreased, while available pores (pF 1.8～3.0) and fine pores (pF 4.0 or more) increased.