Abstract
The soil of the paddy field of Uso-river basin in Kotoh town, Shiga prefecture generates the very stable suspension when the paddy field is puddled. That causes a serious environment problem. The auther investigated the reason why the puddled suspension is so stable and contains so much suspended substances from the stand point of particle size distribution and dispersion-flocculation condition of the suspension. The two factors are considered to be the reasons. One is that this suspension is in a chemically dispersive condition. The other is that the soil increases clay size particles when it is mechanically disturbed. In order to flocculate the dispersed puddled water, the chemical condition of flocculation was estimated using the hetero coagulation theory. In the calculation, the particles are supposed to be spherical, because the main clay mineral of the soil is Halloysite. The entimated flocculation condition was in good agreement with the experimental results. The Calcium ion concentration higher than 0.001mol/dm3 was found to flocculate and clarify the suspension.
