抄録
To make clear whether the serious occurrence of Helminthosporium leaf spot or "Akiochi" in the south-western parts of Japan is accelerated by the abnormal plant nutrition due to high night temperature of air or not, two experiments were carried out in 1951 : in one experiment influence of night temperature treatment for a month after heading upon the growth and nutrition of rice plant was studied, and in another experiment quantities of nutrients absorbed by rice during 24 hours after 10 a. m. September 14 were determined under different night temperature conditions. The results of the experiments are as follows : - (1) High night temperature treatment for a month after heading speeded up the ripening of plant and also retarded the normal development of grains, resulting in the loss of yield. The treatment also diminished the percentage contents of potassium and silica in stems and leaves, and increased the susceptibility to Helminthosporium leaf spot (Table 1). (2) Both high and low night temperature of air reduced the absorption of nutrients in the order K2O>, SiO2>, NH3-N>, MnO>, P2O5 (Table 2). Therefore it is suggested that both supra-optimal and low night temperature retard the normal aerobic metabolism of root and cause the reduction of ions absorption according to the order of hydration. (3) From these results the serious occurrence of Helminthosporium leaf spot or "Akiochi" in the south-western parts of Japan may be attributed in part to the absorption inhibition of some nutrients such as potassium and silica caused by high night temperature.
