SILICA IN SOIL SOLUTIONS: I. THE FORM AND CONCENTRATION OF DISSOLVED SILICA IN AQUEOUS EXTRACTS OF SOME SOILS

Abstract

The effects of method of equilibration, soil-water ratio, pH, and temperature on the form and concentration of dissolved silica in soil-water mixtures were studied and some hypotheses concerning the role of soluble silica in soil development were evaluated in the light of the information obtained.Studies of methods of equilibrating soil-water mixtures showed that, with medium- and coarse-textured soils, shaking for a month resulted in increasing concentrations of dissolved silica with time. Concentrations of dissolved silica in similar mixtures that were allowed to stand were much lower and they changed very slowly with time after a few days. Shaking techniques are not suitable for obtaining equilibrium water-extracts of some soils.Concentrations of dissolved silica in water extracts of the soils studied increased with temperature and with soil-solution ratio, and decreased with increasing pH. The dissolved silica concentration of extracts of different soils ranged from less than 1 to more than 20 p.p.m. Monomeric silica, presumably Si(OH) 4 , was the form of dissolved silica in all of the extracts studied. This result discounts hypotheses of soil genesis involving silica sol.