Studies on the Effects of Soil Temperatures on Rice Plant Growth : 2. Effects of soil and water temperatures upon heading of rice plants

Abstract

This paper deals with the effects of soil and water temperatures upon the heading time and growth regulating substances in leaf sheath of rice plants. A variety named Norin No. 41 was used. The outline of each experiment and results obtained are as follows. 1) From the 6th leaf stage to the heading time, plants were placed in soil thermostats which were kept constantly at 30°, 25°, 20°and 15°C respectively. In addition to these, a plot was subjected to 30°C for the first ten days and then transferred to 15°C. Plants headed earlier as the soil temperature was held higher. A plot transferred to 15°C after ten days treatment with 30°showed a rather striking promotion of heading as compared to 15°constant. 2) Plants were treated with different soil and water temperatures for 10 days at the 3rd, 4th, 5th and 6th leaf stages. The heading promotion was most conspicuous in the plot treated with 30°C, at the 6th leaf stage. The rate of leaf emergency was promoted strikingly by the higher temperatures, so that it resulted in the decreased leaf numbers on the main stem. 3) The growth regulating substances occuring in the top of plants treated were assayed by the Avena-test at periods from 6th to 12th leaf stage. The substances occured much more in quantity as the test temperature rose. This fact might be somewhat related to the heading promotion in the high temperature plots. Moreover the substances were diminished most remarkably at the 7th leaf stage.