Status and Behavior of Sodium and Magnesium during Leaching of Local and Non-Saline Soils

Abstract

Two different sites in northern Iraq (Bashiqa and Hawija) were selected based on their varying rainfall patterns and land use characteristics. Soil samples were collected from the topsoil (0-30 cm) of the study sites, and undisturbed natural soil columns were taken to the same depth (0-30 cm) and with a diameter of 8 cm Three samples per site . Well water and Tigris River water samples were also collected from the same study areas. A laboratory experiment based on miscible displacement was conducted. The soil columns were moistened with Tigris River water and well water to a pore volume of one (PV 1). The moistening and drying process was repeated every ten days until the pore volume reached ten (PV 10). The soil columns were then washed using intermittent leaching after the completion of the moistening and drying cycles for each type of water (Tigris River water and well water) used for moistening and leaching. The results showed that the salt concentration increased at both study sites after the completion of ten wetting and drying cycles. The electrical conductivity values increased to (1.30 - 10.3) dS m⁻¹ at the Bashiqa and Hawija sites when using river water, respectively. However, when using well water, the electrical conductivity values increased to (3.4 - 17.8) dS m⁻¹ at the Bashiqa and Hawija sites, respectively. The results also showed that the amount of aggregated magnesium was higher than the amount of sodium in both cases, whether using river or well water. Furthermore, the results indicated that the release velocity coefficient for sodium was higher than that of magnesium, according to the power function equation. The leaching process using river water was initially rapid, accompanied by a rapid decrease in the electrical conductivity of the effluent and an increase in pore volume at both study sites (Bashiqa and Hawija) up to pore volume 8, at which point the leaching curve stabilized and the slope ended. This indicates the dissolution of all easily soluble salts and most of the trace salts. The solubility, however, the path of the leaching curve using well water behaved differently at the site (Bashiqa), where the leaching path curve rose. This indicates a rise in the concentration of salts at the site during the leaching process instead of a decrease. The reason for this is that the well water has a high concentration of salts  (3.5 dS m-1). At the site of Hawija, the values of electrical conductivity decreased slightly, which is considered insufficient because the value of electrical conductivity did not reach the critical limit at which the soil is considered non-saline (4 dS m-1).