Effect of low salinity water on salt displacement in two soils

Abstract

Two soils - sand and sandy loam - were leached with four displacing solutions in a laboratory experiment. The initial salinity of the saturation extract was 8.0 and 8.4 dS m −1 for the sandy and sandy loam soil, respectively and the electrical conductivity ( ec) of three synthesized solutions (NaCl + CaCl 2) was 2.1, 1.4, and 0.55 dS m −1 at sar = 5 , whereas the fourth solution (0.1 dS m −1) consisted of distilled water. The solutions were used in sequence from high to low ec value. The total volume of leachate with the sandy soil was about 44 pore volumes ( pv) compared to about 21 pv with sandy loam soil in order to reach an equilibrium with the lowest ec solution used. The time required for that equilibrium was 7.3 and 668.5 hours for the sandy and sandy loam soil, respectively. The lower hydraulic conductivity ( K) and the long time required to equilibrate the sandy loam soil with low salt solution increased the leaching efficiency due to the complete mixing between the displacing and displaced solution before displacement occurs. On the other hand, the high K and the short time needed to equilibrate the sandy soil caused partial mixing between the solutions, and decreased the leaching efficiency. In both soils the low salinity water reduced the water movement and it took a large volume of water to lower the ec of leachate to a certain level. Therefore, the use of low salinity water for irrigation should be handled with care.