Effects of soil sodicity, gypsum application, and filtration disposal on hydraulic conductivity under irrigation with domestic effluent water

Sewage water is one of the important water resources for agricultural irrigation in regions where are short of freshwater resource. By leaching experiments of soil columns in laboratory, the effects of soil sodicity, desulfurized gypsum application, and effluent filtration disposal on hydraulic conductivity in silt loam soil under irrigation of domestic effluent water were studied. Five treatments were designed: 1) domestic effluent leaching of soil that was equilibrated with sodium adsorption ratio (SAR) 0; 2) filtrated domestic effluent leaching of soil equilibrated with SAR 0; 3) domestic effluent leaching of soil equilibrated with SAR 30; 4) filtrated domestic effluent leaching of soil equilibrated with SAR 30; 5) domestic effluent leaching of soil equilibrated with SAR 30 plus 0.5% desulfurized gypsum application. The experimental results indicated that saturated hydraulic conductivity decreased with increasing leachate volume, but the steady hydraulic conductivity in nonsodic soil was about 74% greater than that in sodic soil (ESP≈30). Gypsum application at a rate of 0.5% decreased pH and SAR of soil solution, and increased steady hydraulic conductivity by 37% comparing with that without gypsum application for the sodic soil. Filtration disposal of domestic effluent water increased initial hydraulic conductivity in nonsodic soil but decreased that in sodic soil; however, filtration disposal had little influence on steady hydraulic conductivity for both soils. Hydraulic conductivity in sodic soil decreased with increasing soil depth, and it was greater in about 20 cm of soil depth for nonsodic soil. When domestic effluent water is used to irrigation, gypsum application can effectively improve hydraulic conductivity of sodic soil.