Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : CV. On the low temperature resistance at the reduction division stage of rice plants grown under the V-shaped rice cultivation

摘要

In the previous papers5'6'7) the authors reported that under laxuriant growth conditions the restriction of nitrogen supply during the period from 70 to 90 in the leaf-number index brings about not only improvement of plant types but also favourable chemical compositions of the plant, and, as a result of it, the percentage of ripened grains as well as the yield of rice is much increased. (This rice-cultivation method has come to be widely known as the V-shaped rice-cultivation.) On the other hand, if the rice plant is subjected to the low temperature (lower than 17°C) at the reduction division stage, the number of non-fertillized grains is tremendously increased. The authors therefore, considered that in this case the favourable chemical compositions (such as a high C/N ratio) of the rice plant grown under the V-shaped rice cultivation would serve to decrease the number of non-fertilized grains. Following up this argument, the authors grew rice plants with restricted nitrogen supply during the period from 70 to 90 in the leaf number index, and further subjected the rice plants to a low temperature (16-17°C) at the reduction division stage f or 3 days or 7 days, and finally examined the percentage of non-fertilized grains of the plants thus treated, comparing with that of non-treated plants for three seasons. The results obtained may be summarized as follows. 1. The number of non-fertilized grains due to the low temperature is much larger in the 7-day-treatment than in the 3-day-treatment, and the percentage of non-fertilized grains (the ratio of the number of non-fertilized grains to the total number of grains) is always smaller on the nitrogen-restricted plants than on the non-treated plants regardless of the number of grains per panicle. 2. The sum of the number of non-fertilized grains and that of degenerated grains is also larger in the 7-day-treatment than in the 3-day-treatment, and its ratio to the total number of differentiated grains (spikelets) (the number of survived spikelets plus the number of degenerated spikelets) is always smaller on the nitrogen-restricted plants than on non-treated plants. 3. From the result mentioned above it has likely been proved that the restriction of nitrogen supply during the period from 70 to 90 in the leaf-number index serve to increase the low temperature resistance of the rice plant at the reduction division stage. Moreover, one reason of it has been ascribed to the favourable chemical compositions such as a high C/N ratio in the plant. (See table 3.) 4. The heading date is delayed by 1.5 days in the 3-day-treatment and by 3 days in the 7-day-treatment, while it is promoted by 4 days in the nitrogen-restriction treatment.