CALCIUM- AND SULFATE-ION CONCENTRATIONS IN A SOIL RECEIVING EXCESS GYPSUM, AS INFLUENCED BY SEVERAL FACTORS

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Abstract
The effects of varying soil-water ratios on the Ca-, Mg-, and SO4-ion concs. in a soil containing 0.17 mole of CaCl2 for each 2 kg. of soil are reported in table 3. The small change in conc. of SO4 ion in the presence of increasing concs. of Ca ion can be explained by the increasing solubility of gypsum in the presence of increasing concs. of Mg ion, which varied almost directly with the Ca-ion cones. As the soil-water ratio decreased, the conc. of readily soluble salts also decreased, resulting in a progressively smaller effect on the solubility of gypsum. The approx. direct proportion existing between the SO4 ion remaining in soln. and the amt. of water present becomes evident when the millimoles per kg. of soil are compared. The deviations from a true direct proportion, as would be expected from a very slightly soluble salt in water, are accounted for by the ionic strengths resulting from the other electrolytes in the soil, concs. of which change with the soil-water ratio. The differences in the total amts. of SO4 in the 1:1 and 1:2 extracts, and various concs. of HC1 were added to lots of soil containing an excess of gypsum. The effect of varying water content on a soil system containing a given amt. of CaCl1 and an excess of gypsum was explored over a wide range of soil-water ratios. The concs. of Ca and SO4 ions found are, within reasonable limits, explicable in terms of solubility-product and ionic-strength phenomena.

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