ABSTRACT
Soil salinization is a major environmental hazard that limits agricultural production. Using sewage sludge and recycled wastewaters in amelioration of saline-sodic soils is one of the most effective ways to dispose waste. However, a very low initial permeability of soil in the freeze-thaw conditions can make improvement difficult. Therefore, column experiments at a soil depth of 15 cm have been conducted to determine the effects of the combination of four stabilized sewage sludge doses (0, 50, 100, 150 t ha-1), three freeze-thaw cycles (0, 5, 10 times) and two water types (FW: freshwater, RWW: recycled wastewater) on gypsum-treated saline-sodic soil properties. The effects of non-saline-sodic RWW on the soil properties were similar to the FW in total 22.5 cm leaching amount. Compared to gypsum alone and initial values, sewage sludge increased wet aggregate stability, organic matter, total N and exchangeable Ca + Mg while it decreased pH, exchangeable Na and CaCO3. Saturated hydraulic conductivity was not induced by sewage sludge although exchangeable sodium percentage and electrical conductivity were reduced by 44% and 63.6%, respectively. Negative effects of freeze-thaws on hydraulic conductivity and salinity and sodicity elimination were not observed, while pH and aggregate stability were negatively affected from ten freeze-thaws. Overall, it can be concluded that the improvement of hydraulic conductivity is attributed to the further improvement of soil structure from more strong wet aggregate stability via additional sewage sludge and leaching amounts.
