Simulating water and salt movement in tile-drained fields irrigated with saline water under a Serial Biological Concentration management scenario

We report on the analysis of water and salt balance data collected at a tile-drained experimental site irrigated with saline groundwater. Saline groundwater (EC = 8.4 dS/m) was applied to an area planted to replicated blocks of redgums (Eucalyptus camaldulensis) and tall wheat grass (Lophopyrum elongatum). The intercepted drainage effluent was disposed off-site to an evaporation pond. The experiment applied the concept of Serial Biological Concentration (SBC) of salt, which aims to reduce drainage effluent volumes from irrigated land. Data collected during the 2002-2003 irrigation season were used to calibrate the soil-water-atmosphere-plant (SWAP) model. SWAP satisfactorily simulated components of the water and salt balance when compared to the collected hydrologic data. The simulation results show that the soil EC resulting from the high applied-irrigation EC reduced crop evapotranspiration ETc and that the redgum trees produced (marginally) smaller drainage volumes of a higher salinity than tall wheat grass pasture and thus can be considered as better crops for SBC design. Simulations over a 10-year period highlight that a large proportion of the applied saline drainage water escapes below the level of the tile drains, thus reducing the concentration effect of the trees and pasture. Much of the water intercepted by the tile drains under the site was resident groundwater, rather than leachate from underneath the crops. The paper also discusses site characteristics and management options that would be favourable to more effective SBC designs.