Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : LXXXVIII. Combined effects of air-temperature and water-temperature seedling periods on the characteristics of seedlings of rice plants (In case of seedlings treated for different number of days during which the seedlings attained an identical leaf-age)

Abstract

The first necessity to obtain high yields is to raise healthy and strong seedlings. The authors, therefore, have hitherto reported seversl papers concerning on this point (LXXV, LXXVIII, LXXXI and LXXXIV). In the present paper, growing the seedlings under each condition of all possible combinations of air-temperatures (16°C, 21°C, 34°C and 36°C) and water-temperatures (16°C, 21°C, 31°C and 36°C) for different number of days during which the seedlings attained identical leaf-ages (4.5, 6.0, and 7.5), the authors examined the effects of air-temperatures and water-temperatures on the characteristics of seedlings of rice plants. The results can be summerized as follows. 1. The progress of leaf-emergence is much more influenced by water-temperature than by air-temperature, and the higher water-temperature rises, the faster the rate of leaf emergence advances. 2. The value of integrating water-temperature for attaining an identical leaf-age has been proved much smaller under favourable water-temperature (31°C) than under low water-temperatures (16°C or 21°C) in spite of the value having hitherto been considered almost identical under any temperature above 10-16°C. 3. In case of all identical leaf-aged seedlings being compared with each other, the top dry-weight, the leaf-area, the rate of net assimilation, the number of tillers and the ratio of top dry-weight to the height of seedlings (T/H) are all largest under the condition of 31°C or 21°C in air-temperature and 16°C or 21°C in water-temperature, and smallest under the condition of a low air-temperature (16°C) and high water-tempere (36°C). 4. The nitrogen content of an identical leaf-aged seedlings is largest under the condition of 16°C in air-temperature and 36°C in water-temperature while the carbohydrate contente is largest under 16°C in water-temperature in any air-temperature. 5. The amounts of nitrogen as well as carbohydrates of an identical leaf-aged seedlings per plant are largest under the condition of 31°C in air-temperature and 16°C in water-temperature on account of the amounts being much more influenced by the dry-weight than by the contents of seedlings. 6. From the present experiment a low water-temperature such as 16°C, which affects directly the growth points of seedlings has been re-confirmed to be quite important for raising healthy and strong seedlings.