Abstract
We found a phenomenon that, when an aqueous solution of a polymer having carboxyl groups such as polyacrylic acid is percolated into soil from its surface, insolubilized matter of the polymer accumulates as a membrane in the soil resulting in an impermeable layer. We carried out experiments of the layer formation in soil columns on various soil conditions, and investigated effects of soil codition on the formative phenomenon of the impermeable layer. The results are as follows. 1. The impermeable layer was formed deeper in a soil as the packing density of the soil decreased, and the layer did not form in soil with a bulk density below a certain value.2. Regardless of the water content of a soil, the impermeable layer was formed at the same depth in the soil.3. Formation of the impermeable layer seems to require the following two conditions : one is that the amount of exchangeable calcium ion of the soil is 1 cmol(+) kg^<-1> or more and the other is that permeability of the soil is not too low.4. The less exchangeable calcium there was in a soil, the deeper the impermeable layer formed in the soil ; when the amount of exchangeable calcium was less than 1 cmol(+) kg^<-1>, the layer was not formed in the soil.5. The impermeable layer was not formed in Tottori sand dune soil because of a small amount of exchangeable calcium in it, 0.3 cmol(+) kg^<-1>. When calcium ion was added to Tottori sand dune soil to the extent of 0.9 cmol(+) kg^<-1>, the impermeable layer came to be formed in the soil.6. When the polymer solution was fed into a hollow of a soil surface and it percolated into the soil without the effect of a wall of a soil column, a hemispheric impermeable layer was formed in the soil.7. In a layered soil having a lower layer of fine soil particles, the impermeable layer was formed at the depth in the soil above or just at the boundary of layers, and it was not formed below the boundary. This result shows that the impermeable layer is formed by filtrating the solution with insolubilized polymer.8. The impermeable layer seems similar to the spodic horizon formed in nature. In both phenomena, an aqueous solution of organic substances infiltrates or percolates into a soil from its surface, the organic substances accumulate in a soil with polyvalent cations, and the organic substances have carboxyl groups.
