Use of Freeze-Thaw Purified Saline Water to Leach and Reclaim Gypsum-Amended Saline-Alkali Soils

Saline-alkali soils adversely affect both the construction of ecological landscapes and crop production in coastal areas. This study aimed to investigate the effects of freeze-thaw process on purifying saline water, and evaluate the potential of combining saline ice melt-water leaching and gypsum addition for remediating coastal saline-alkali soil. Saline water with a salinity of 10 g L-1 was tested in this study, and the leaching experiment included four treatments: saline water direct leaching (S), saline water direct leaching combined with gypsum application (SG), saline ice melt-water leaching (SI), and saline ice melt-water leaching combined with gypsum application (SIG). The results showed that more salts were concentrated in the bottom ice layer than in the other ice layers after the saline water was completely frozen. The salinity of the melt-water decreased during the melting process, and the mean salinity of melt-water during the second half of the melting process was significantly lower than the salinity of source water samples. During the leaching phase, the cumulative leachate losses of Na+, Ca2+ and Mg2+ were significantly greater for the SI treatment than that for the S treatment. After leaching, the soil electrical conductivity (EC) significantly decreased, and the SI treatment exhibited better performance than the S treatment in terms of reducing the soil EC and sodium adsorption ratio (SAR). The application of gypsum improved the soil saturated hydraulic conductivity (K-s) and decreased both the soil pH and alkalinity when the coastal saline soil was leached by the saline ice melt-water.