Salt dynamics in soil profiles during long-term evaporation under different groundwater conditions

To study salt dynamics in soil profiles under different groundwater conditions, a 3-year indoor experiment was carried out under conditions of open-air evaporation. Silt loam soil was treated under three groundwater table depths (0.85, 1.05, and 1.55 m) combined with three groundwater salinities: 0.40 dS m^? 1 (2 g l^? 1), 0.80 dS m^? 1 (4 g l^? 1), and 1.60 dS m^? 1 (8 g l^? 1). A total of nine soil columns (0.14 m internal diameter) were used to simulate different combinations of groundwater depths and salinities. The results obtained showed that salt first accumulated at the bottom of the soil column, and only when soil salinity in this layer had remained relatively stable with time, salt began to accumulate in the adjacent upper soil layers. When all subsoil layers had reached dynamic salinity equilibrium, electrical conductivity (EC) of soils in the surface layer began to increase drastically. With increasing salt accumulation in the surface soil, EC of the subsoil began to rise tardily. The further up the soil layer, the earlier EC started to increase, although the redistribution of salts in the soil profile tended to be homogenous. Groundwater depth did not significantly change subsoil EC values at the same depth; however, it distinctly affected the time needed for the subsoil to reach dynamic salinity equilibrium. Groundwater salinity, on the other hand, did not significantly alter the time point at which soil salinity at the same depth began to increase rapidly or the time period needed to reach dynamic salinity equilibrium. This study explored salt transport processes in the soil profile through a long-term experiment, enabling us to reveal some general laws governing salt dynamics that will be very important to understand the mechanism of soil salinization. The results could be further used to set up strategies to prevent salinization or to improve salt-affected soils.