Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : LXXVIII. Rooting ability of rice seedlings, which were raised under different air- and water-temperatures, after transplanting. (In case of seedlings treated for an identical number of days in seedling period.)

Abstract

Growing rice seedling for 30 days under each condition of all possible combinations of air-temperatures (16°C·21°C·31°C and 36°C) and water-temperatures (16°C·21°C·31°C and 36°C) and transplanting them again under each condition of all the combinations of air- and water-temperatures as mentioned above, the authors examined the relation of rooting ability of the seedlings to growing conditions in the seedling period and the characteristics of seedlings. The results obtained might be summarized as follows. 1. The number of roots newly emerged, the length of roots newly elongated, the number of leaves newly died and the numbes of leaves newly emerged on the main stem after transplanting were investigated, as indexes of rooting ability, on the 10th day after transplanting. 2. As a result of examining the relation between rooting ability and growing conditions in the seedling period, the number of roots newly emerged after transplanting appeared to be mainly influenced by water-temperature not by air-temperature in the seedling period, and it showed the largest value on the seedling grown under the water-temperature of 31°C. On the other hand, the largest value in length of roots newly elongated was found on the seedlings grown under low water-temperatures such as 16°C or 21°C. The number of leaves newly died after transplanting was much less on the seedlings grown under low water-temperatures than on those grown under high water-temperatures, and the number of leaves newly emerged on the main stem was larger on the seedlings grown under low air- and water-temperatures than on those grown under any other air- and water-temperature. 3. As a result of examining the relation between rooting ability and temperature conditions during the rooting period, rooting ability appeared to be mainly affected by water-temperature not by air-temperature on any index of rooting ability, so the most desirable value was obtained at 31°C and the most undesirable value was found at 16°C of water-temperature on any index of rooting ability. 4. The seedlings, which showed the most desirable values on all the four indexes of rooting ability and also showed actually highest rooting ability under the most conditions during the rooting period, appeared to be raised under the combined condition of relatively low air- and water-temperature such as air-temperature 21°C and water-temperature 16°C, air-temperature 21°C and water-temperature 21°C, and air-temperature 31°C and water-temperature 16°C in the seedling period. 5. The seedlings, which showed the most undesirable values on all the four indexes of rooting ability and also showed actually lowest rooting ability under the most conditions during the rooting period, appeared to be raised under the highest water-temperature, i. e. 36°C, in the seedling period. 6. The characteristics of seedlings which showed high rooting ability seemed to be small in plant age, in number of roots and in ratio of the weight of leaf-blades to the weight of leaf-sheaths, but large in content of chlorophyll in leaves.