Developing guidelines for the length of drying-off of irrigated sugarcane before harvest in the Burdekin

In irrigated sugarcane production, water is usually withheld prior to harvest to dry the field and make it trafficable for harvesting operations, and to raise both the sucrose content of the cane and sucrose yield. The severity of drying-off required to produce the maximum return will depend on the trade-off between the increase in sucrose content and the reduction in cane yield. In this paper, a crop-soil model and long-term climate data are used to determine the economically-optimum duration of drying-off for irrigated sugarcane at Ayr, Austral ia, for a range of harvest dates and soil types. This duration varied with harvest date and soil type (range 29 to >150 days). When dryingoff for a given duration, there are some seasons when, due to climatic variability, drying-off is not long enough or is too long. Overall, it will be shown that drying-off to achieve a 4% reduction in cane yield in 50% of seasons seems to minimise risk. The model output is also used to indicate a likely rule-of-thumb for drying-off management that could be applied across soil types and harvest times taking account of rainfall during the drying-off period.