Studies on the effects of temperature of irrigating water upon the growth and yields of rice plant

Abstract

1) The main object of this experiment is to make sure whether the high temperature of irrigating water in the daytime of midsummer in the Kyushu region is harmful to rice plant or not and also to examine it's possibility of being a cause of “AKI-OCHI”.2) The rice plants were grown in 12 plots. They were divided into 3 plots according to the kind of treatment. Plot A: the irrigating water was kept hot about 40°C only in the daytime and kept in natural state daring the night. Plot B: the irrigating water was kept cold about 2°C merely in the daytime and kept in natural state during the night. Plot C: the check plot in natural state throughout all the day.Each plot was subdivided into 4 plots according to the period of treatment. Aw, Bw, Cw plots were treated from the early tillering stage till the heading. A1, B1, C1 plots were treated from the early tillering stage till the stage of highest number in tillers. A2, B2, C2 plots were treated from the end of A1, B1, C1 treatment till one week after ear formation period. A3, B3, C3 plots were treated from the end of A2, B2, C2 treatment till the heading. (Aw, A1, A2 and A3 plots are of dummy treatment.)3) The growth in plot A was suppressed during the treatment, but recovered soon after the treatment. The color of leaves became deep when the treatment began and the effect continued for a long time, and the heading came a little later. Most of the leaves therein had been kept green for 20 days after the heading and they began to wither a little later, but those in plot B a little earlier. The difference of the yield between plots A and C was not significant, and the yield in B plot was less than in C plot.The difference of the yield with the treated periods was not significant, but there was a tendency that plots Aw and Bw were slightly inferior, and plots A1 and A2 were a little superior to check plot.4) The harmful period of high temperature observed under natural conditions corresponds roughly to the period of treatment in plots A1 and A2. Precise conclusions can not be obtained unless the field experiment is carried out but the results of this experiment seem to show that the natural high temperature of irrigating water in midsummer in the Kyushu region has not a bad effect upon the rice plant.Cultivating race plants in constant temperature, many eminent investigators have obtained the results that the optimum temperature of irrigating water for rice plants is 30-34°C, and the temperature over 36°C is extremely harmful, and that the temperature 39°C shows only very meager growth. But it has been found that when the irrigating water is kept about 40°C in the daytime and in natural state during the night, the high temperature has not a remarkable bad effect upon the rice plant.