Studies on the effects of high water temperature during daytime and night upon the growth and yields of rice plants. : 1. Top growth of the rice plants as affected by high water temperature.

摘要

For the second crop of paddy rice in Okinawa, the temperature of irrigation water seems to be an important problem in relation to the causes of low productivity. In order to study the influence of high water temperature (35℃) on the growth of paddy rice, experiments were carried out by varying temperature in day and night. The results obtained are as follows: 1. In case of constant high water temperature (35℃), during day and night the growth of rice plant was remarkably retarded. Retardation of growth was also found for either high temperature in daytime only or in night only. 2. Though the number of leaves on main stem was increased in high water temperature (35℃), the boot-leaf appears at the same time or earlier than in natural water temperature, as the leaf appearance cycle in earlier period was hastened. 3. The treatment by high water temperature shortened the length of leaf-blades, especially, the elongations of leaf-blades grown immediately after transplantation, of upper leaves on main stem, and of first leaf on the tillers were shortened significantly. 4. The effects of high water temperature over the number of tillers and panicles were evident. When the water temperature was kept high day and night, the number of tillers reduced remarkably. When the difference of water temperature m daytime and night was large, the number of tillers increased, and when the water temperature was kept high at night the number of panicles decreased. 5. In high water temperature, the tillers developed from higher loci, and the ratio of panicles to tillers decreased. 6. Heading date was accelerated by the treatment of high water temperature.