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Some factors affecting the extraction of sulphate from selected Lower Fraser Valley and Vancouver Island soils

University of British Columbia

A study was undertaken to determine some of the factors which affected the extraction of sulphur from seven selected soils of the Lower Fraser Valley and Vancouver Island; with particular reference to the effect of pH, concentration and cation of phosphate buffers. In all cases the presence of phosphate resulted in more sulphur being extracted, than extraction with water only. In every instance increasing the concentration of neutral sodium phosphate buffers from 0.005M to 0.5M resulted in increasing sulphur extraction. Using a 0.5H sodium phosphate buffer and increasing the pH from 4 to 8 generally resulted in maximum extraction at pH 7, except notably in the Langford soil in which the amount of sulphur extracted increased as the pH was changed from 4 to 8. The behaviour of four surface soils when extracted with 0.5M sodium phosphate at varying pH levels was quite similar, the mineralogy of the <2µ fraction was also similar. Gel filtration studies of the 0.5M phosphate extracts of the Langford showed that at pH 4 little inorganic sulphate was extracted, while from pH 6 to 8, the amount extracted remained almost constant, though more than three times that extracted at pH 4. The extracted organic fraction increased as the pH varied from 4 to 8. In soils with a low carbon content and a high content of free iron and aluminum oxides, the water extractable sulphur was very low, as was the amount of phosphate extractable organic sulphate. The amount of sulphate extracted from the original air dry samples by 0.5M phosphate was very much less than the sulphate adsorbed from a 50 ppm sulphur solution. It was found that a neutral 0.5M sodium phosphate solution extracted more sulphur in nearly all cases, than other extractants, and in the soils studied cold water did not seem suitable. The neutral 0.5M phosphate solution extracted inorganic and a portion of the organic sulphate and may be expected to be a suitable chemical extractant which will be able to indicate the sulphur status of soils of the Lower Fraser Valley.

Text

2012-03-28

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http://hdl.handle.net/2429/41846

Soil Science

University of British Columbia

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