Effect of silicon compounds on microbial transformations in soil.

A study was made of the effects of adding a range of silicon compounds (of potential use as fertilizers) to a variety of different soils. In addition the solubilization of insoluble silicon compounds by bacteria and a species of Penicillium isolated from ferns growing in walls (as a likely silicon-rich environment) was determined. The results of the present study show that: 1) Bacteria solubilize rock potash, releasing free silicon into the medium. 2) Growth of a Penicillium Sp. in vitro increases the solubilization of sodium silicate, but concentrations of free silicon decrease when the fungus is grown in the presence of silicic acid and rock potash presumably duet o Si-immobilization by the fungus. 3) Water-extractable silicon increased when either silicic acid or rock potash was added to all soils, under both aerobic and anaerobic (waterlogged) conditions. 4) Liming increased the release of soluble silicon from sodium silicate, silicic acid and rock potash the effect being seen in all soil types. 5) Silicic acid generally decreased bacterial numbers in all soils, at least over the first 14 days of the incubation period. 6) Silicic acid and rock potash had no effect on nitrification, while the addition of sodium silicate stimulated nitrate production, this effect is assumed to be largely due to the resultant marked increase in soil pH. 7) Addition of silicic acid and rock potash led to increased sulphur oxidation. 8) The addition of silicic acid to the agricultural loam soil led to a decrease in arylsulphatase and ehydrogenase activity, as well as respiration and soil biomass.