Modelling irrigated sugarcane crop under seasonal climate variability: a case study in Burdekin district

Sugarcane industries worldwide are exposed to uncertainty associated with weather and seasonal climate variation. This variability often impacts negatively on crop production, leading to conservative farming strategies that sacrifice productivity in order to reduce the risk of losses in poor years. The situation is especially severe in Australia where sugarcane production is subject to an extremely variable climate. Inter-annual variability in climatic properties in Australia is about 15–18% higher than any other major agricultural nation. In such an extremely variable environment, knowledge of crop performance under different climate conditions and use of seasonal climate forecasts in decision making can play an important role in supporting agricultural risk management. Here, we quantified the effect of seasonal climate variability on sugarcane performance under rain-fed conditions and irrigation by integrating the long term climate data record into a crop model, the Agricultural Production Systems SIMulator (APSIM) Sugar, which was calibrated using case study information for the Burdekin sugarcane production region. Two irrigation schedules of five and 20 days were simulated for a range of irrigation water volumes applied in each irrigation event to the plant crop and four ratoons to study the effect of irrigation timing. We conducted economic analyses to convert biophysical yield results into economic returns which were classified according to annual precipitation terciles i.e. wet, normal, and dry climate conditions. This framework allowed us to identify optimal irrigation strategies to achieve maximum yield or economic return under different climate conditions. The results showed that seasonal climate has a strong influence on crop performance and cash flow in both rain-fed and irrigated sugarcane in the Burdekin region. The case study example was not economically viable under normal and dry climate conditions for either the rain-fed or limited water volume simulations, which indicates the significant importance of using seasonal climate forecasts in irrigation scheduling decisions. Different optimal irrigation strategies associated with different climate conditions were observed for all cropping stages (i.e. the plant crop and four ratoons). Results also showed that more regular irrigation resulted in better water use efficiency in terms of both yield and economic benefits. Yield and economic benefit increases for the 5 day irrigation schedule can be up to AUD 40 t ha−1 and AUD 1000 ha−1, respectively, compared with those for the 20 days schedule