Sulfate and Gypsum Determination in Saline Soils
1987
Skarie, R. L. | Arndt, J. L. | Richardson, J. L.
Despite advances in instrumentation for direct determination of SO²⁻₄, many investigators analyzing saline soils continue to estimate SO²⁻₄ by difference between the sums of major cations and anions and to measure gypsum by methods that avoid direct SO²⁻₄ determination. The present study compares SO²⁻₄ in saturation extracts as estimated by difference with SO²⁻₄ measured by single-column ion chromatography for saline Aeric Calciaquolls and Typic Haplaquolls in eastern North Dakota. Results should be applicable throughout the Northern Great Plains. For extracts of sulfatic, saline soils, estimation of SO²⁻₄ by difference compared favorably with SO²⁻₄ determined directly. Results were more variable for highly chloridic soil extracts because errors from other methods were large relative to the amount of SO²⁻₄ present. Gypsum was determined by using a sufficiently dilute extract to completely dissolve the gypsum present in the soil sample. Gypsum content was calculated in two ways, based either on Ca²⁺ or SO²⁻₄ measured in the dilute extract. For highly chloridic soils, gypsum contents based on Ca²⁺ determination were essentially equal to the results based on SO²⁻₄ data. For sulfatic soils, gypsum contents were lower when Ca²⁺ values were used due to loss of Ca²⁺ to the exchange complex during the extraction process.
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