Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice

Abstract

Growing the rice seedlings under the conditions of all possible combiations of air-temperatures (16, 21, 31, and 36°C) and water-temperatures (16, 21, 31 and 36°C) up to the age of 6.5 in leaf-number, and transplanting those seedlings again under the same various temperature conditions mentioned above, the authors investigated (a) the number of roots newly emerged, (b) the length of roots newly elongated, (c) number of dead leaves and (d) the number of leaves newly emerged on the main stem at the time of 10 days after transplanting, and furthermore examined the most suitable temperature conditions for both production of seedings with high rooting activity and vigorous rooting in the rooting period after the transplanting. 1) In the seedling period the air-tempertures suitable for vigorous root development were 21°C, 31°C and 36°C, and the water-temperature suitable for increasing the number of roots was 31°C and that suitable for elongation of root length was 16°C. In the rooting period the water-temperature had much more powerful effect on root development than the air-temperature and the water-temperature for increasing the number of roots was 36°C and that suitable for elongation of root length was 31°C 2) The seedlings grown under low air-temperatures and low water-temperatures had few-number of dead leaves after transplanting, and low air-temperature and high water-temperatures in the rooting period served for decreasing the number of dead leaves after transplantig. 3) The temperature conditions in the seedling period had little effect on emergence of new leaves on the main stem, while the water-temperature in the rooting period had a great effect on it and the water-temperature of 31°C was most suitable for increasing the number of new leaves on the main stem. 4) The temperature condition of the combination of the air-temperature of 21°C and the water-temperature of 16°C was liable to produce the seedlings which showed the most favourable result in rooting, as far as the four studying items on rooting activity mentioned above were concerned, in any temperature condition in the rooting period, and in the second place that of the air-temperature of 16°C and the water-temperature of 16°C followed. These facts suggested that the low temperature such as 16°C was quite necessary to raise strong and healthy seedlings. 5) The combination of the air-temperature of 21°C and the water-temperature of 31°C in the rooting period was liable to let every seedling show the most fovourable result in rooting on all the four items concerning rooting activity mentioned above, and in the second place that of the air-temperature of 31°C and the water-temperature of 31°C followed.