Effect of Irrigation Water pH on Saturated Hydraulic Conductivity and Electrokinetic Properties of Acidic, Neutral, and Alkaline Soils

The demand for the use of marginal-quality water as an irrigation resource is increasing in arid and semiarid region lands due to the freshwater shortage. Marginal waters usually have high salinity and high alkalinity and may contain high proportions of ions such as sodium. This study investigated the impact of irrigation water pH on saturated hydraulic conductivity (K-s), cation exchange capacity, net particle charge, and dispersivity of soils. Nine soils with differing pH, alkalinity, clay content, and mineralogy were used in leaching column experiments, with solutions of varying sodium adsorption ratio (20 and 40), electrical conductivity (0.8, 1.5, 2.5, 5, 10, 25, and 50 dS m(-1)), and pH (6, 7, 8, and 9). The desired pH was achieved by adjusting the HCO3-/Cl- ratio and CO2 partial pressure using CO2 gas with 99.9% purity. Results showed that the increase of solution pH causes an increase in net negative charges on clay particles, resulting in higher exchangeable cations, negative zeta-potential, and clay dispersion and movement of dislodged particles into pore spaces, resulting in K-s reduction. This effect was more evident for acidic and low-clay-content soils. The K-s reduction in relation to pH was less for smectitic and high clay content soil than for kaolinite dominant soils for all concentrations, suggesting resiliency of the smectitic soils under irrigation water with high pH. Results reinforce that it is essential to consider the original pH, clay content, and mineral of the soil and the pH, electrical conductivity, and sodium adsorption ratio of the irrigation water to accurately predict the K-s reduction of the soil.