On the Temperature of Irrigation Water and the Growth and Yield of Rice Plant in the Area Irrigated with Cold Water in a Good Harvest Year

Abstract

In Miyagi Prefecture, 1955, the rice yield was increased as much as 126 per cent of the average year yield, and the increasing rate of yield was different from each other for villages. Then we investigated these rates in areas irrigated with low temperature water. The results obtained were as follows:(1) Several villages through out our county showed the different rates in their increasing yields. As a tendency in general, the increasing rates of rice yield in the villages obtaining good harvest in ordinary year were low, but, on the contrary, in the villages with poor harvest these rates were high and in the latter it was indicated in the figure of 30-40 per cent. Such tendency was recognized in the area irrigated with cold water, too. The larger the ratio of paddy field with cold water in each village, the higher was the increasing rate of rice yield.(2) In the mountaneous area the climatic conditions during that summer were favorable for the growth of rice plant, and such trends were recognized strikingly on the maximum temperature of air, daily range of air temperature and a number of fine days.(3) As an example of field observation in area with cold water we may present the data on the temperature of irrigation water in the Okura River Basin. According to those data the water temperature in that area was much warmer, so that the effect of cold water for the rice yield was much less than in Shichigashuku-mura, 1954, that is to say, in the Okura River Basin the effect of cold water disappeared in the 20 per cent of the irrigated space in the paddy field.We might consider that the higher increasing rate of rice yield was obtained because during the summer the climatic conditions and the temperature of irrigated water were favorable for the growth of rice plant.