Analysis of Yield-Determining Process and Its Application to Yield Prediction and Culture Improvement of Lowland Rice : LXII. Effects of irrigation-water temperature under different water-depths on the growth, grain yield and yield-components of rice.

Abstract

In the previous report, the authors pointed out that the damages of rice plants caused by high and low water-temperatures at the stage of young panicle formation were much heavier than those at the booting stage under the general water-depth (3-4 cm) and presumed that the fact could be mainly ascribed to the difference in submergence of the young panicles between the two stages. By subjecting the rice plants at different growth stages to different combinations of water-temperatures and water-depths, the authors tried to prove the above mentioned presumption and also to clarify the effects of the treatments on the growth, yield and yield-components. 1. Effects of the water-depth on the plant height and the number of tillers were clearly seen when treated at the tillering stage, showing as a rule the deeper the water-depth the higher the plant height, and the fewer the number of tillers. 2. In the periods of differentiation and development of young panicles, high (37°C) and low (15°C) water-temperatures caused the development of young panicles as well as the elongation of internodes to arrest and made the plant to produce the late emerging tillers and to kill young panicles inside the tillers (only high temperature) and furthermore to decrease the values of yield-components and yield. The effectiveness of high and low temperatures on rice plants differed with the developmental stages of young panicles as well as water-depths, and the ill-effects were quite severe in any water-depth and no relation was found between the ill-effect and the water-depth at the stage of young panicle formation, in particular under the high water-temperature, while at the booting stage only slight ill-effects were found under the shallow water-depth and as the water-depth increased the plant was more seriously damaged, i.e. a direct proportion was found between the water-depth and the ill-effect (Fig. 1, 3, 4). 3. As the result of investigating the relation between the vertical positions of the young panicles and the water-surface on the initial and final dates of the treatments, it was found that all of young panicles were always below the surface of water in any water-depth at the stage of young panicle formation, while at the booting stage most of the young panicles were above the water-surface under the shallow water-depth (2 cm) and the number of young panicles below the water-surface increased as the water-deepened (Fig 2). 4. From the relation between the vertical positions of young panicles and the water-surface the effectiveness of high and low water-temperatures on the rice plant in particular on the development of young panicle could be fully understood. It may be safely concluded, therefore, that the differences of the damages caused by high and low water-temperatures between the stage of young panicle formation and the booting stage under the general water-depth are mainly brought about by the difference of the relation between the vertical position of young panicles and the water-surface, namely, the difference in submergence of young panicles.