Physiological Studies on the Effects of Silicic Acid upon Rice Plants : XI. Effects of various amounts of silicic acid supply on the growth of rice plants and essentiality of silicon

Abstract

Experiment I. The increase in the growth of rice plants by the addition of silicic acid (SiO2) of 0, 0.5 1, 5, 20, 100 and 300 ppm respectively, to the cultural solution was tested. In the case of lOO ppm or less, the higher in SiO2 concentration, the greater in the dry weight of rice plants. While little or the differences were observed among the effects of the addition of SiO2 of 0.5, 1 ppm and non-SiO2 on the growth of rice plants. In this test it was recognized that the addition of SiO2 from 50 to 10O ppm was suitable for the growth of rice plants. Experiment II. The essentiality of silicon to rice plants was discussed in this experiment which was carried out in 1967. The materials used were: distilled water which was passed through the ion exchange resins (Amberlite IR-120B and IRA-410); beakers, pipets and mess cylinders made of plastics, and other materials the same with those cited in the previous reports. 7'9) Hulled rice of Norin No. 6 were sown and grown on the bed made of plastics. After transplanting them to the pots (made of vinyl chloride) the rice plants in non-SiO2 plot were grown in the phytotron (regulated at about 30∼33°C at daytime, but stopped to regulate at night). Sodium ions were eliminated by passing sodium silicate aqueous solution through ion excgange resin Amberlite IR-120, and SiO2 (100 ppm) was added to the cultural solution in control plot. To protect the rice plants in non-SiO2 plot from adhesion of the drops pf guttation containing silicic acid coming from the rice plants in control plot, the latter were cultured in another place (glasshouse). The results obtained are as follows: Dry weights of the harvest are shown in Table 1, Ratio of dry weights of the harvest between non-SiO2 plot and control plot was 91% per plant, and dbout 80% per panicle. Content and percentage of silicic acid absorbed in rice plants are shown in Table 2. The percentage of silicic acid content in the rice plants in non-SiO2 plot showed so low as one figure down from the smallest value obtained up to now. The color of chaffs of the rice plants containing 0.0025% SiO2 was of deeper dark-brown than that of the chaffs of rice plants containing O.O6% SiO2, and the ripened grains of the former were smaller in size than those of the latter, but they were small. Little or no difference was observed among the growth of rice plants containing 0.13∼0.20% SiO2. There was no any great and essential difference between the growth of rice, plants containing O.2% SiO2 and that of rice plants containing O.0025% SiO2. From these facts, it might be concluded that silicon may not be regarded botanically as essential element to rice plants, but regarded as essential element to rice plants from agronomical viewpoint.