Evaluation of the potential use of langbeinite (potassium sulfate / magnesium sulfate) as a reclaiming material for sodic and saline sodic soils.

Abstract

Soil sodicity/salinity and scarcity of water are important constraints of agricultural development in arid lands. Excessive exchangeable sodium of sodic and saline sodic soils cause swelling of clays and dispersion of colloidal particles, and results in poor soil-water-air relationships. Reclaiming sodic and saline sodic soils involves the displacement of exchangeable sodium and its subsequent leaching from the root zone. This further depends upon the choice of chemical or cation to exchange for sodium and the quality and availability of water for leaching. Therefore, a series of experiments including soil characterization, laboratory batch studies, column leaching studies and greenhouse crop response studies were conducted to evaluate the potential use of langbeinite as a reclaiming material for saline sodic soil. Both the Grabe clay loam and the Guest clay soils met the requirements of a saline sodic soil category. The Grabe clay loam was more strongly saline sodic than the Guest clay soil, and was therefore used in the subsequent studies. In the batch studies involving a 1:1 soil:water extracts, langbeinite proved to be more efficient than gypsum in replacing exchangeable Na especially at higher levels of applied amendments. In the column studies, the amount of exchangeable Na displaced due to gypsum and langbeinite was the same when high amount (4 pore volumes) of water was used for leaching. However, langbeinite removed considerably higher amounts of sodium than gypsum with the use of lower volumes of leaching water. Accordingly, savings of over 9 acre-inch of irrigation water per acre of reclaimed land can be realized by using langbeinite over gypsum to lower the ESP of the soil to about 10% when both amendments are applied at a rate of 12 tons/ha. The hydraulic conductivity (HC) of the soil increased significantly due to application of both gypsum and langbeinite and decreased due to leaching with increasing pore volumes of water. Although steady state HC was not attained with the use of gypsum, the HC of the soil treated with gypsum was higher than the langbeinite treated soil after leaching with 4 pore volumes of water. Similarly, seed germination and dry matter yield of lima bean plants responded to the application of gypsum and langbeinite and leaching both with Safford irrigation water and Tucson tap water. Such responses both to the amendments and volumes of leaching water were of a higher magnitude with langbeinite than with gypsum.