水稲収量成立原理とその応用に関する作物学的研究 : XLIX. 生育各期の水温の高低並びにその日較差の大小が水稲の生育収量及び収量構成要素に及ぼす影響

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Responses of the growth, grain-yield and yield-constitutional factors to the irrigation-water temperatures and their daily ranges were examined by subjecting the rice plants to different combinations of controlled day and night water-temperatures for 15 days (1957) or 30 days (1958) in different growth stages, as seen in Table 1. 1. Effects of the daily ranges of water temperatures on the number of panicles were clearly seen when treated at tillering stages, and the number of panicles the more increased in the higher day water-temperatures and in the lower night water-temperatures. 2. Low water-temperatures always affect the plants to increase the number of tillers and to reduce the plant height, and high day water-temperatures combined with a night temperature of 25°C were most effective in increasing the plant height. 3. There were found negative correlations between the number of panicles and that of spikelets per panicle, and between the percentage of ripened grains and the total number of spikelets per hill, then the clear effects of water-temperature on the number of spikelets per panicle and the percentage of ripened grains could hardly be seen. 4. The weight of 1, 000 grains was much increased by high day and night water-temperatures in the period from the beginning stage of spikelet differentiation to the heading stage. 5. The grain yield was much favored by high water-temperatures such as 35°C and 30°C in daytime and at night throughout the entire period. And it was very noticeable that a low night water-temperature as low as 15°C does not reduce the yield as well as the percentage of ripened grains markedly even in the critical period, if only day water-temperatures are kept pretty high. 6. Low water-temperatures than 27.5°C in an average of day and night temperatures caused the rice plants to delay their heading dates as the water-temperatures fell off.