Impact on soil hydraulic properties resulting from irrigating saline-sodic soils with low salinity water

Irrigation-induced salinity is a serious problem facing irrigated areas in the Murray-Darling Basin of Australia. Groundwater pumping with farm re-use for irrigation is a key strategy for controlling salinity in these irrigation areas. However, the re-use of highly saline-sodic groundwater for irrigation leads to accumulation of sodium in the soil profile and can result in sodic soils. Leaching of saline-sodic soils by winter rainfall and low salinity irrigation waters are 2 management scenarios likely to exacerbate sodicity problems. Characteristic to sodic soils is poor soil structure and potentially reduced soil permeability. Two indicators of soil permeability are infiltration rate and hydraulic conductivity. A replicated plot experiment was conducted to examine the long-term impact of irrigation with saline-sodic water on soil permeability. High levels of soil sodicity (ESP up to 45%) resulted from 10 years of saline irrigation. Over this period, leaching by winter rainfall did not result in long-term impacts on soil hydraulic properties. Measured soil hydraulic properties increased linearly with the salinity of the applied irrigation water. Leaching by irrigating with low salinity water for 13 months decreased soil salinity and sodicity in the topsoil. The resulting reduction in steady-state infiltration indicates soil structural decline of the topsoil. This trial shows that groundwater re-use on pasture will result in high sodium levels in the soil. Sodicity-related soil structural problems are unlikely to develop where there is consistent groundwater irrigation of pasture. However, structural decline of these soils is likely following the cessation of groundwater re-use.