Effects of Phosphorus and Acidity on Levels of Silica Extracted from a Palouse Silt Loam
1987
Concentrations of Si found in soil solutions are affected both by soil pH and by P availability. Consequently, it was hypothesized that the heavy local use of NH₄-based N fertilizers and of P fertilizers could greatly affect the Si chemistry of soils from the Palouse area of northern Idaho. The objectives of this study were to evaluate the effects of P and acidity on concentrations of Si in water extracts from Palouse silt loam (fine-silty, mixed, mesic, Pachic Ultic Haploxerolls) soils and to correlate observed effects with possible mechanisms responsible for Si solubility, Soil samples were equilibrated with acid and with P for periods of 0.2 to 150 d in 0.02 M CaCl₂ solutions. Increased acidity and the presence of P were both found to increase the concentrations of Si in solution above control levels. These data appear to be additive, suggesting that the mechanisms responsible for increasing solution Si levels for the respective treatments are different. It is postulated that acidity increases Si concentrations in solution by directly affecting the solubility of compounds containing Si, and that P oxyanions compete directly with Si compounds for specific sorption sites.
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