Biochar, manure and superabsorbent improve the physical quality of saline-sodic soil under greenhouse conditions

The increasing salinization and sodification of soils in drylands and irrigated systems present a great challenge to agricultural production and threaten soil quality. There is an urgent need to investigate potential strategies to remediate soils that are threatened by these processes. To address this challenge, the current study investigated the effects of organic and inorganic amendments and leaching fraction (LF) on physical and hydraulic properties including the soil water characteristic curve (SWCC), Dexter's index of soil physical quality (S-Dexter), bulk density (BD), saturated hydraulic conductivity (K-s), and water repellency index (RI) in a saline-sodic soil. A greenhouse experiment was carried out in a completely randomized design with two factors (amendment and LF). The amendments included superabsorbent (1%) (SA), zeolite modified with CaCl2 (2%) (ZC), biochar (2%) (B), biochar + manure (2%) (BM), and a control (no amendment) (CT), and combined with two levels of LF (15% and 30%). Spring wheat (Triticum aestivum, 'UG99') was planted in the soil columns. After harvest, undisturbed samples were collected from each column for the determination of soil properties. The results demonstrated the effectiveness of the SA and organic amendments to enhance K-s and decrease BD. There was a significant (p < 0.01) positive effect of the amendments, particularly biochar and superabsorbent on the soil pore size distribution. The SA amendment significantly increased soil water retention, especially at high matric potentials (i.e., 0 to -80 hPa). The effect of organic amendments on the SWCC was in between those of the ZC and SA amendments. The SA and BM treatments were sub-critically water repellent, while the ZC treatment increased soil water repellency. The SA, B, and BM15 treatments exhibited very good physical quality (S-Dexter > 0.05). The relative air and moisture capacities were optimal in the B-amended soil at field capacity (matric potential -330 hPa). We conclude that B, BM, and SA are suitable amendments for reducing the adverse effects of salinity and sodicity via an improvement in soil physical quality.