Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : LXXI. Combined effects of air-temperatures and water-temperatures at different stages of growth on the growth and morphological characteristics of rice plants.

Abstract

Following the previous report (LXX), the authors futher examined the combined effects of air-temperatures and water-temperatures at different growth stages on the growth and morphological characteristics of rice plants by using the same method as in the previous report (LXX), and obtained the following results. (1) The increase in the number of tillers during each treated stage is little affected by air-temperature, but much by water-temperature. The maximum increase in the number of tillers is found at 31°C at Stage I (rooting stage), at 36°C at Stage II (tillering stage), at 16°C and 36°C at Stage III (panicle initiation stage), respectively. (cf. Table 2) (2) The increase in plant height at Stage I is not influenced by air-temperature, but only by water-temperature, and its effectiveness for increasing the plant height is found as the following order, i.e., 31°C>36°C>21°C>16°C. At Stage II and III both air-temperature and water-temperature have serious effects on increasing the plant height, and the order of their effectiveness for increasing it is also found as follows, i. e., 31°C>36°C>21°C>16°C. At Stage IV both air-temperatureand water-temperature still affect the increase of plant height, but in this case the effectiveness of air-temperature is a little stronger than that of water-temperature. (cf. Table 2) (3) The plant age in leaves is much more effectively increased by water-temperature than by air-temperature, and the plant age is markedly increased by high water-temperatures such as 31°C and 36°C, while it is little increased by low water-temperatures such as 16°C and 21°C. (cf. Table 2) (4) The total number of leaves on the main stem is little affected by air-temperature, but much affected by water-temperature. In particular it is most severely affected by the water-temperature at Stage II (tillering stage), and it is likely to be the more increased by the higher temperatures so far as the experiment is concerned. (cf. Table 2) (5) The number of days required by the plant from the transplanting time to heading time is little affected by air-temperature, but much affected by water-temperature in the early growth period (Stage I and II), and it is also remarkably affected by both air-temperature and water-temperature in the middle growth period (Stage III and IV), but it is affected only by air-temperature in the late growth period (Stage V). In any growth period a temperature of 31°C (in air as well as in water) is most effective in hastening the heading time, while a temperature of 16°C is most effective in delaying it, so far as the present experiment is concerned. (cf. Table 2) (6) Cnmbined effects of air-temperatures and water-temperatures at different stages of growth on the length of main culms, panicle length and the length of each leaf-blade, leaf-sheath and inter-node from the uppermost one to the downward 5th one have been examined. As a result, it has been clarified that the air-temperature or water-tempeture at particular stage has a conspicuous effect on lengthening a particular leaf-blade, leaf-sheath and inter-node and also the length of main culms as well as that of panicles. In other words, close relationships have been found between morphological characteristics and temperature (air or water) at particular growth stages. These relationships will be effectively used on diagnosing the defect in the rice cultivation by a morphological examination of the hills of rice. (cf. Table 2) (7) The present results, together with those given in the previous report (LXX), have been suggested to play a significant role in improving rice cultivation as well as in forecasting the yield of rice.