SIMULATION OF BRACKISH WATER FLOW AND SALT ACCUMULATION IN LOAMY SAND

Irrigation with saline water adds dissolved salts to soil. Higher levels of sodium and chloride in soil are toxic to crops such as vegetables and cotton. To understand effects of brackish water irrigation on the soil salinity and underlying groundwater quality, authors used Hydrus-1D code to simulate brackish water infiltration and salt transport in a loamy sand soil based on soil column test conducted in a greenhouse environment. First a flow model was established with the observation data of the soil column test. The hydraulic parameters were calibrated with observed moisture data and flow patterns were characterized based on simulation. Highly permeable loamy sand allow irrigated brackish water easily infiltrate through the column and may cause immediate impacts on groundwater if the groundwater surface is shallow. The flow model was then used as the base for the transport model to simulate salt movement inside the column. Results of salt transport simulation showed that the position of the sodium (Na+) front was mildly retarded relative to that of chloride (Cl-) due to Na adsorption on soil exchange complex. Based on predicted Na+ curves in the soil profile, loamy sand retained Na+ and Cl- within the top 20 cm depth. This suggests that the applied Na+ would be retained within the upper profile. The simulated pattern of Na+ accumulation in the top 20 cm of the soil profile agreed with observation collected after the end of six irrigation cycles. The study showed that irrigation with brackish well water having EC of 2.3 dS m-1 may cause salt accumulation at the top soil to some extent.