Assessing the impact of recycled water reuse on infiltration and soil structure

Soil sodicity, salinity, clay dispersion, and clay soil cracking are significant issues for modern agriculture, especially in arid and semi-arid regions of the world. Sodium adsorption ratio (SAR) has traditionally been used to estimate potential changes in infiltration rates or hydraulic conductivity when sodium cations dominate irrigation water quality. Recent research indicates that the cation ratio of soil structural stability (CROSS_f and CROSS_opt) provides better predictive capabilities for soil structure and threshold electrolyte concentration than SAR, especially when water used for irrigation or aquifer recharge contains both potassium and sodium cations. In this study, soil columns filled with clay loam were used to assess the impact of recycled water reuse on soil structure stability and saturated hydraulic conductivity. Ten treatments were prepared using chloride solutions of sodium, potassium, calcium, and/or magnesium to create a broad range of synthetic recycled water qualities with varying SAR, CROSSf, and CROSS_opt values. After a pre-saturation process, the columns were maintained to have a constant 1 cm head of treatment solutions with a salinity of 1.5 dS/m. The results showed that CROSS_f had a stronger correlation with saturated hydraulic conductivity and soil aggregate stability in comparison to CROSS_opt and SAR. The R² for saturated hydraulic conductivity and soil structure were 0.90 and 0.94 for CROSS_f, 0.41 and 0.60 for CROSS_opt, and 0.75 and 0.78 for SAR, respectively. Notably, the treatments that received solutions with 0-SAR values but contained potassium had significantly more dispersible clay throughout the entire soil column than the treatment that received calcium chloride solution. It was concluded that the CROSS_f model could offer enhanced accuracy and insight into predicting the impact of recycled water reuse for irrigation on soil infiltration rate and soil aggregate stability.