Leaching and reclamation of calcareous saline-sodic soil by moderately saline and moderate-SAR water using gypsum and calcium chloride

Lysimeter experiments were conducted with sandy-clay-loam soil to study the efficiency of two amendments in reclaiming saline-sodic soil using moderately saline and SAR (sodium-adsorption ratio) irrigation water. Gypsum obtained from industrial phosphate by-products and reagent grade Ca chloride were applied to packed soil columns and irrigated with moderately saline (ECe = 2.16 dS m(-1)), moderate-SAR water (SAR = 4.8). Gypsum was mixed with soil prior to irrigation at application rates of 5,10,15, 20, 25, and 32 Mg ha(-1), and Ca chloride was dissolved directly in leaching water at application rates of 4.25, 8.5, 12.75, 17.0, and 21.25 Mg ha(-1), respectively. The highest application rate in both amendments resulted in 96% reduction of total Na in soil. The hydraulic conductivity (HC) of soils receiving gypsum increased in all treatments. The highest HC value of 6.8 mm h(-1) was obtained in the highest application rate (32 Mg ha(-1)), whereas the lowest value of 5.2 mm h(-1) was observed with the control treatment. Both amendments were efficient in reducing soil salinity and sodicity (exchangeable-sodium percentage, ESP); however, Ca chloride was more effective than gypsum as a reclaiming material. Exchangeable Na and soluble salts were reduced with gypsum application by 82% and 96%, and by 86% and 93% with Ca chloride application, respectively. Exchangeable Ca increased with increasing amendment rate. Results of this study revealed that sodium was removed during cation-exchange reactions mostly when the SAR of effluent water was at maximum with subsequent passage of 3 to 4 pore volumes. Gypsum efficiently reduced soil ESP, soil EC, leaching water, and costs, therefore, an application rate of 20 Mg ha(-1) of gypsum with 3 to 4 pore volumes of leaching water is recommended for reclaiming the studied soil.