Studies on the seepage water control in the warm area paddy field

The irrigated paddy rice fields must have a proper degree of seepage. And this seepage must be properly adjusted and controlled depending on the season. Also, it can be understood that the work of adjustment and control must be done in different manners depending on whether it is to be done in the high water temperature areas in warm districts or in the low water temperature areas. From these points of view, it should be noted in planning irrigation works for the existing paddy rice fields that the water requirement in depth must be adjusted to a proper level taking into account the weather conditions, and in the fields with too low water requirement in depth, such as the plans of Chikugo and Saga, appropriate works must be built to raise it to a proper level. Particularly in the latter case, the water requirement in depth will decrease further owing to works using machinery. When the irrigation works are planned, it must be taken into account that it is necessary to control the water at a proper level meeting the requirements of the water needs at each stage of the growth of the plant because it is expected that the rice yield will decrease due to the reasons stated above. Next, examples and effects in Japan will be described, concerning the water control. (1) Seepage-water control facilities of culvert style Mr. Terashi OIE is a farmer in Chizuka-machi, Buzen-city, Pref. Fukuoka. This region is located along the coast of Setonaikai, and has suffered drought for 4 years: 1958, 1959, 1960 and 1961. For those damages, he designed a circulating irrigation system having the culverts as are described below, and applied it in his paddy rice fields. Since that time water-shortage has been solved during a long drought. And moreover, this had remarkable increase in the cropping. So the facilities not only have dissolving effect against the water-shortage but also controlling effect on the seepage water. (Fig. 5) (2) Seepage-water control facilities of gate style This is a so-called Chikasui-dome, a gate type facility, in the Chiba prefecture. It consists of water-level controlling gates located at the important points of the main and lateral drainage canal. The water-level is raised or lowered by operating the gate in order to regulate the seepage-water coming from the paddy field. (Fig. 6