The effect of contact time, extractant type, and soil to extractant ratio on gypsum determination by Acetone method

Document Type : Research Paper

Authors

Soil and Water Research Institute, Agricultural Research, Education, and Extension Organization, Karaj, Iran

Abstract

Gypsum is spread in soils of arid and semi-arid regions and controls the soil physiochemical properties when it exists as the main soil component. Due to the undesired effects of gypsum in agriculture and plant growth, the accurate determination of its concentration is very important for soil classification and land use management. In this study, the parameters affecting the gypsum determination by the acetone method, namely contact time, extractant to soil ratio, and different extractants, were investigated. Results revealed that the gypsum dissolution reaction was fast and most of the gypsum was dissolved in less than 0.5 h. Gypsum extracting with high extractant to soil ratios (1:200) had led to underestimation in the gypsum concentration. So that, the measured gypsum at 0.5 h extraction in soils with 10, 20, 30, 40, 50, 60, 70, 80, and 100% gypsum was underestimated by -1, 3.5, 9.6, 11.0, 22.4, 29.3, 39.6, 47.5, and 87.8% (according to the actual content) respectively. Decreasing the extractant to soil ratio to 1:400 overestimated (10 to 50%) the gypsum in the samples containing less than 50% gypsum. NaCl, KCl and MgCl2 solutions increased the gypsum solubility eliminated the underestimation in gypsum determination especially in 1:200 ratio. However, the use of salt solutions as extractants in the natural soils had led to overestimation at the higher extractant to soil ratios (1:400). The critical electrical conductivity (EC) in the measuring of gypsum by the Acetone method was 1000 µS/cm. According to the results, use of deionized water as the extractant, 0.5 h contact time, and variable soil to water ratio according the soil gypsum content and to reach the EC of lower than 1000 µS/cm were the optimum condition for determination of soil gypsum by the acetone method and therefore is recommended.

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