IRRIGATION SCHEDULING IN SUGARCANE BASED ON ATMOSPHERIC EVAPORATIVE DEMAND

Increasing water use efficiency continues to be a significant challenge for the Australian sugar industry. Irrigated agriculture faces ever-increasing pressure to grow more from fewer inputs, and hence at lower cost, to remain viable. Increasing community awareness of environmental issues has raised expectations for irrigators to use bestpractice management to minimise off-site impacts and maximise productivity from a scarce resource such as water. Irrigation water is used most efficiently when crop requirement is defined accurately and water is applied to meet this demand both fully and at precisely the right time. Crop water requirement is based on crop response to water deficits, as well as atmospheric evaporative demand (AED) for water. In this paper, we develop two alternative scheduling techniques that utilise simple tables and computerised systems based on AED, knowledge of crop response to water stress, and soil water holding capacity. An example of the simple scheduling tables developed for growers in the Ord region of Western Australia indicated that irrigation should be as frequent as 10 days prior to the wet season and as infrequent as 21 days after the wet season, depending on soil type and ratoon date. The computerised AED based water balance technique was applied to three growers in the Burdekin, and it showed how scheduling with this technique could have improved the effectiveness of their operations.