Solute movement through undisturbed calcareous and dry region soils under differing water flow velocities

The use of low-quality irrigation water in arid regions ensures the reconstruction of diverse physical and chemical dynamics in the soil profile. The objective of this study was to examine the efficacy of two water flow velocities of tap and sodic water for characterizing ion exchange of colloidal particles. Undisturbed samples were taken into the plexiglas columns with 40 cm in height and 6.9 cm in diameter from the dry area of Konya, Turkey. Two different water sources with varying qualities, tap water and poor quality sodic water (ESP≈20, obtained by preparing solution from analytically pure NaHCO₃), were applied to the top of the columns as leaching water in two water flow velocities; close to saturated hydraulic conductivity (Ks) (fast, saturated condition) and unsaturated condition (slow). The number of the columns with duplicated experiments was 8. In each leaching, a quarter pore volume (350 ml) of water was regularly applied and leachates were collected from the outlet of columns. The water flux in the soil column decreased faster in the fast leaching application than in slow leaching as the sodic irrigation water was applied. This shows to destructive effect of Na+ on inner surface of water flow channels in the soil. Gradual increases for the pH of the leachates in both water quality and velocity experiments were detected. The EC of the leachates dropped very fast at the beginning of leaching in both water quality applications, and then, became steady. No effect of tap water treatment on Ca⁺² contents of the leachates was observed. However, sharp decreases in Ca⁺² concentration were detected at the beginning of sodic water application, and then remained constant. All sodic water applications caused an increase in Na+ concentration of leachates till the end of treatments. In slow leaching applications, the increase in Na concentration in the leachates was slower compared to those of the fast leaching. While Ca⁺² concentrations in the leachates remained constant with tap water applications, although the soils are calcareous. Ca⁺² was transported remarkable high at the beginning of the sodic water application. As the leaching progressed, transport of Ca⁺² from the soil continued constantly due to the Na-Ca exchange processes. The effects of different leaching treatments were clearly observed from the pH-EC, Ca⁺² and Na⁺transports. Consequently, sodic water application caused significant changes in the pH values of the soils with the effect of time, and this effect was expressively marked from the changes in the salt and sodium contents of the soils.

Keywords: flux, ion exchange, leaching, saturated and unsaturated leaching, solute transport, water flow velocity

Acknowledgement: This work was supported by the Scientific and Technological Research Council of Turkey [Project number: TUBİTAK-118Y343].