Towards effective control of deep drainage under border-check irrigated pasture in the Murray-Darling Basin: a review

Abstract

High watertables and land salinisation threaten the sustainability and prosperity of the irrigated dairy industry in the Murray–Darling Basin of Australia. High watertables and salinisation result from excessive deep drainage. Spatial and temporal trends in deep drainage data pertinent to the dairy industry in the Murray–Darling Basin are reviewed with a view towards reducing deep drainage. The reviewed data indicate that deep drainage under border-check irrigated pasture is generally greater than the leaching requirement and can be reduced without affecting pasture growth. Deep drainage through levee soils is likely to contribute significantly to regional groundwater. Consideration needs to be given to the appropriateness of using the border-check irrigation system on levee soils. Pressurised irrigation systems or land use change may be required to reduce deep drainage under these soils. The majority of deep drainage under floodplain soils occurs during winter and spring, when rainfall exceeds pasture water use. Developing a soil water deficit prior to winter will reduce deep drainage. This can be achieved by ending the irrigation season earlier. A later start to the irrigation season also offers potential to divert more winter rainfall into evapotranspiration rather than deep drainage.