Abstract
For establishing a method of decreasing the damage of rice plant caused by low irrigation-water temperatures, the authors examined the effects of non-water-logging in every half-day period or a whole period at the different growth stages of the plant on its growth, grain yield and yield-components and compared the effects with those continuously water-logged with an optimum and a low temperature under a field condition as well as potted conditions. Results obtained might be summarized as follows: 1. At the stage just after transplanting every non-water-logged plot was much poor in rooting and in growth at an early stage than that water-logged with an optimum water temperatur, on account of that the former was lacking in soil moisture in spite of being high in soil temperature. 2. Both at the tillering stage and the stage from spikelet differentiation to heading, the potted plants grown under the non-water-logged condition with soil moistures higher than P.F. 1.70 (in the value of tension-meter) were higher in grain-yield than those grown under an optimum water temperature as well as under a low water temperature on account of the fact that in the non-water-logged plots the number of panicles and spikelets per hill much increased (Fig. 1.). On this occasion it is likely worth noticing that the rice plants subjected to non-water-logging showed a relatively high percentage of ripened grains in spite of a remarkable increase in the number of spikelets per hill, because in general there exists a negative correlation between those two components. The fact may be ascribed to the favorable effects of the non-water-logged treatment on the soil condition, nutrition and conseqently to carbon assimilation activity of rice plants. Furthermore, it is also presumedly noteworthy that no unfavorable effect of non-water-logged treatment was observed in the important period from the spikelet differentiation stage to the heading stage in which in general a deep water-logging practice has hitherto been recomended to farmers. 3. At the ripening stage potted rice plants grown under non-water-logged condition were a little lower in the percentage of ripened grains and in yield than those under watter-logged condition, while the plants grown under the field condition did not show such a tendency at all. 4. The non-water-logged treatment carried out during the whole growth period brought forth worse effects in yield as well as in growth than those brought forth by the water-logged treatment even with a low water temperature. It will be necessary, therefore, to examine not only the accumulative effect of non-water-logged treatment through the whole growing period but also the effects of that as influeneed by different kinds of soil, soil moisture etc. From the results above mentioned it should be taken into consideration that the non-water-logged cultivation for some period is quite effective not only for decreasing the damage due to cool irrigation water but also for saving the amount of water which is now becoming a new problem in our country.
