Comparative evaluation of amendments for remediation of brine-affected saline-sodic subsoil

Anthropogenic soil salinization threatens agricultural productivity and ecosystem health. This study evaluated gypsum, polyacrylamide (PAM; solid and solution forms), biochar, peat, NanoBind (NB), Liquid Fulvic (LF), Liquid Organo Hume (LOH), and Humalite for remediating brine-affected, saline-sodic subsoil. Sequential benchtop incubation and column leaching experiments were used to evaluate changes in saturated hydraulic conductivity (Ks), sodium adsorption ratio (SAR), sodium leaching efficiency, and selected soil physicochemical properties before and after leaching. Full-rate gypsum was the most effective treatment, increasing Ks and decreasing SAR from 22 to 6. Combined with leaching, gypsum enhanced sodium removal, with 83% of the sodium mass removed after the application of three pore volumes of water. Liquid Fulvic combined with 25% of the gypsum requirement sustained increased Ks, although it did not improve salt removal. Most amendments reduced SAR to some extent, but gypsum was the only treatment that consistently remediated the soil to regulatory standards. Biochar and peat increased soil organic carbon but had limited effects on Ks or SAR. PAM applied in solution improved Ks without increasing sodium leaching, whereas solid PAM reduced hydraulic conductivity. Gypsum with adequate leaching was the most effective treatment for remediating saline-sodic soil, whereas PAM with reduced gypsum rates may offer a more cost-effective alternative. However, boron persisted in the soil longer than soluble salts and exchangeable sodium, indicating that boron may represent a critical constraint to the complete remediation of brine-affected soils, with further research needed to improve boron attenuation in brine-affected soils.