Abstract
Puddling is the most important practice under the transplanted rice culture. The object of this study is to clarify the mechanism of percolation control by puddling in the laboratory experiment using three types of soil. In this paper, consideration was given to this based on the results of the changes in the soil surface and in the hydraulic head differences. The results are summarized below:
1. In clayey soil, the soil consolidation developed slowly, and over a long time from the lower part of the mixed layer to the upper part, and consequently, the flow rate was slowly reduced.
2. In medium-textured soil, it was considered that the sudden reduction in the flow rate just after the mixing was caused by the consolidation in the lower part of mixed layer and the filling of the consolidation layer and just below the mixed layer with fine particles.
3. In coarse-textured soil, the flow rate after the mixing was quickly reduced with the hindered. settling and the sedimentation rate of which was approximately constant. The flow rate after the sedimentation was influenced by the movement of fine soil particles and the filling with them.
4. The lower the permeability at the subsoil and the larger the dispersion of mixed soil, the longer the time which the hindered settling and the consolidation continued was. As a result, the flow rate kept decreasing over a long period of time.
