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

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 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 HSO 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.