Effect of physical amendments on salt leaching characteristics for reclamation

- A slower water movement is associated with a greater salt leaching efficiency.
- A greater rate of cation exchange can increase salt leaching.
- Addition of bentonite can improve the reduction of soil salinity.

Saline-sodic soils may be reclaimed through the addition of amendments to alter the soil pore system and hydraulic functions, therefore allowing salts to be leached from the soil. For the purpose of investigating the suitability of specific amendments for improving leaching and reclamation, soil percolation column studies were conducted to assess the influence of amendments on cation exchange, the potential for the release of cations and changes in hydraulic conductivity of the soil. A fine textured saline-sodic soil amended separately with 20% wood chips (wt/wt), 40% fine sand (wt/wt) and 2.5% bentonite (wt/wt) was used for this study as well as a non-amended soil as a control. The impact of amendments was evaluated by continuous leaching of the soil substrates with deionized water until the hydraulic conductivity and leachate chemistry stabilised. The bentonite amended soil had a greater increase (15.9 cmolc kg− 1) in exchangeable Ca2 + and a higher reduction in exchangeable Na+ (12.29 cmolc kg− 1) after the final leaching due to a greater rate of cation exchange for this soil substrate. The bentonite amended soil also had a greater reduction (92%) in Na+ content compared with the other soil substrates. The hydraulic conductivity of all soil substrates improved during leaching although the hydraulic conductivity of bentonite amended soil reduced after three pore volumes of leaching. This study suggests that a slower water movement (an increased percolation time) and a greater rate of cation exchange were associated with the greater leaching efficiency. Therefore, addition of bentonite improves and accelerates the reduction of salinity and sodicity.