Potential for increasing irrigation water use efficiency in northern Australia where watertables are shallow

Shallow water tables can provide substantial contributions towards meeting a crop's water requirement. As water is the major limitation to sugarcane production throughout irrigated areas in northern Australia, upflow from water tables could be used to boost production. Irrigators in the sugar industry are lacking information on how to modify irrigation scheduling to account for upflow where shallow water tables occur. Potential benefits arising from shallow water tables were assessed based on improvements to irrigation water use efficiency and economic benefits to sugarcane growers. This assessment was based on a review of related literature and results of cropping system simulations using SWIMv2.1 for water tables up to depths of 2 m. For three soil types representing a range of saturated hydraulic conductivities found in agricultural soils, modelling results indicate all sugarcane water requirements could be met by water tables at 1m. Below this depth, predicted irrigation requirements were dependent on soil type and rooting characteristics. Magnitude of upflow was better reflected by near saturated hydraulic conductivities as opposed to soil texture. Irrigation scheduling that has been modified to include upflow from shallow water tables should result in significant improvements to irrigation water use efficiency, along with measurable economic and environmental gains.