Changes in soil chemistry after the application of gypsum and sulfur and irrigation with coal seam water

Abstract

Irrigation with alkaline and sodic groundwater, including water extracted from coal seams (CS-water), has the potential to cause environmental harm through the degradation of soil structure. This study evaluated the effectiveness of soil amendment prior to irrigation with CS-water (pH 9.39, sodium adsorption ratio [SAR] 83) on the soil chemical properties of two soils, a Red Ultisol and a Red-Brown Ultisol. Repacked columns of soil were amended with either gypsum alone or with gypsum combined with elemental sulfur (S). These amendments were either surface applied or incorporated to a depth of 20 cm, with columns irrigated with the equivalent of 36 ML ha−1 CS-water. In the Red Ultisol, soil solution SAR was maintained in the desired range of 10–25 in amended soils, which was generally similar to that achieved in control soils irrigated with pre-treated CS-water where the alkalinity had been neutralized with H2SO4 and sodicity ameliorated by dosing with micronized gypsum prior to irrigation. In the Red-Brown Ultisol soil solution SAR values were higher. Surface-application of amendments (soil solution SAR values of 10–40) was more effective than incorporation (soil solution values of 80–120). Soil solution pH decreased with gypsum and S amendment of the Red Ultisol by up to ≤2.0 pH units, despite irrigation with alkaline CS-water. In contrast, soil solution pH was more difficult to maintain in the Red-Brown Ultisol, with pH increasing to ≈8.0 in most treatments. The results demonstrate that alkaline and sodic CS-water can be chemically ameliorated successfully within the soil profile by the addition of gypsum and S amendments, although the efficacy of chemical amendment depends upon the method of incorporation and soil properties.