水稲によるケイ酸のイオンとしての吸収

抄録

Although silicic acid absorption of paddy rice (Oryza sativa L.) is believed to occur mainly in the uncharged and mono-molecu1ar state (Si (OH)_4°), this has not been elucidated theoretically, yet. Better understanding and elucidation of various phenomena related to silicic acid is possible when we think of silicic acid being absorbed in the ionic state ((OH)_3SiO^-). Using this supposition, nourishment composition and cation-anion balance of paddy rice was investigated. As a result, when evaluated by supposing silicic acid as anion, the equivalent ratio of cation and anion was nearly one, and its equivalent relation was found. But when evaluated not supposing silicic acid as anion, the equivalent ratio is four to five, and anion shortages overwhelmingly lose their ionic balance. Also, when considering the chemical state of silicic acid in soil solution by the chemical equilibria theory, silicate ion is calculated to be present at a level of about 10^<-5> to 10^<-7>mol L^<-1>at pH 6 to pH 8. This concentration corresponds to the level of 10^<-6>mol L^<-1>of Km in system 1 of dual mechanism in ionic absorption mechanism in crops, indicating that silicic acid can be sufficiently absorbed in ionic state. As a result, it was strongly suggested that silicic acid absorption of paddy rice is ionic, acting as a counterion of cation.