水田土壌に於ける粘土の生成に関する研究 (第1報) : 稀薄炭酸ソーダ溶液に可溶の珪酸及び礬土の年間消長に就いて

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The contents of silica and alumina in a paddy soil dissolved by dilute solutions (2.0% and 0.5%) of Na_2CO_3 were investigated at several periods during one year. Marked decreases of both SiO_2 and Al_2O_3 which were considered to be in a gel-state occurred soon (about two weeks) after stagnation had started. The decrease may probably be interpreted to be a result of linking between SiO_2 and Al_2O_3 forming new clays. It is felt that an alteration of oxidation condition in soil into a reducing state by stagnation would induce rapidly such a tendency that soluble SiO_2 is gathered concentrately in clay-size fractions, especially in colloidal <0.6μ. After 17 days-stagnation, in 45 days in summer, the distinct increases of both SiO_2 and Al_2O_3 were observed. This may be interpretated that a weathering destruction of minerals already presented and / or newly-formed clays may have been accelerated under high temperature. However, there should be a much more supply of Al_2O_3 resulted from substitution of Al atoms in crystal lattices by Fe^<++> and Fe^<+++> produced in soil than SiO_2,because SiO_2/Al_2O_3 ratios became lower. From August to Octover, only SiO_2 decreased but Al_2O_3 showed some slight increases. We considered that these decreases of SiO_2 probably be resulted from alteration of SiO_2 itself into insoluble forms such as Quartz and / or cristobalite. After harvestry of paddy plants, it was appeared that mineral weathering did not proceed materialy when stagnation was continued uninterruptedly from Octover to February, although clay formation could occur to some extent. However, in Spring, from February to June weathering of minerals proceeded even under stagnation. When soil was drained in Autumn, minerals weathered not only from Octover to February, but also, even more excessively, from February to June. Under freely drained condition. SiO_2-gels formed by intensive weathering could be leached out almost completely, but Al_2O_3 accumulated more and more. Such an abundance of Al_2O_3 gels and a poverty of SiO_2 gels in soils led a soil to much more unfovarable one posessing a lower SiO_2/ Al_2O_3 ratio of clays than that of the preceeding year. Furthermore, it was possible to expect such a condition that paddy plants in the following year would inevitably suffer from a more severe deficiency of SiO_2 at an early stage of growing soon after stagnation. From these investigations, the writers wish to emphasize an importance of a degree of drainage in paddy soils during no-planting period as much as a position of ground-water-level in soil profiles and an easiness of capillary rise of water, because the former will determine a loss rate of SiO_2 by leaching and the latter influences a rate of recovery or enrichment of SiO_2 in a surface layer by resilication.
社団法人日本土壌肥料学会の論文
1955-03-31

水田土壌に於ける粘土の生成に関する研究 (第1報) : 稀薄炭酸ソーダ溶液に可溶の珪酸及び礬土の年間消長に就いて

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