Abstract
The effects of soil type and manuring practice, such as application of organic matter and/or calcium silicate, on characteristics of silica dissolution and adsorption (CSDA) by soils were analyzed by the incubation of soil with several silica solutions. And the possibility of silica dissolution and adsorption parameters (SDAP) as an index of silica supply ability of paddy soils was verified. The following laboratory conditions clarified CSDA sufficiently : Incubation at 30℃ for five days with soil : water ratio of 1 : 10. The difference between initial and final silica concentration in solutions through incubation (y ppm) was linearly proportional to the initial silica concentration in solutions (x ppm) as the following equation : x/a+y/b=1. Constant-a was the silica concentration of solution at which neither dissolution nor adsorption occurred, and constant-b was the silica concentration dissolved from soil into distilled water. This equation was rewritten as the following equations : u/a+v/c=1, c=a・b/(a-b), where u (ppm) is the final silica concentration in solutions, v (mg/100g soil) is the amount of dissolution or adsorption of silica by a unit soil. Constant-c, which was extrapolated, showed the amount of silica dissolved from soil into vast water. The application of calcium silicate did not affect the a of SDAP at all, but affected much the b/a of SDAP. The c of SDAP correlated highly with the silica content of paddy rice, because it explained the silica supply ability under reductive soil condition, such as silica content in the supernatant obtained by the incubation under submerged condition. It also explained the effect of clay mineral and soil texture on silica supply ability.
