SORPTION OF SILICA IN A NORTHERN IDAHO PALOUSE SILT LOAM

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Abstract
Recent research suggested that a plow pan development in Palouse soils of Northern Idaho may be enhanced by deposition of Si compounds. However, the mechanisms responsible for Si sorption in the plow pan zone have not been determined. We undertook this study to: (1) evaluate the differences in Si sorption between profiles with and without well-developed plow pans, and (2) evalute possible mechanisms of Si sorption and associated reaction reaction rates. Soil samples were collected from Palouse silt loam soils (fine-silty, mixed, mesic Pachic Ultic Haploxerolls) both with and without well-developed plow pans. Samples were allowed to equilibrate with solutions containing Si concentrations of 40, 100, and 140 .mu./ml before extraction using immiscible displacement. Silica sorption was controlled by a second-order reaction with variation of reaction constants with depth in the profile. Silica sorption in well-developed plow pans was significantly less than found above and below, probably due to the previous occupation by Si of the most accessible sorption sites. Although the sorption process was found to depend on soil pH, data suggested that the equilibrium Si concentrations found in the plow pan zones were controlled by amorphous Si deposited at the surfacesd of soil particles.

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