Maximising the economic value of water through adaptive, climate-informed irrigation scheduling

Improving water use efficiency (WUE) in agriculture is crucial, given the escalating scarcity of water resources. This study aims to maximise the economic value of irrigation water at the farm level – farming gross margin over the total irrigation water including costs, a concept focusing on economic efficiency rather than the conventional biophysical WUE. We propose an integrated simulation-optimisation analysis that links crop growth responses from simulation by a calibrated APSIM-Sugar model with a novel bio-economic model for optimal irrigation scheduling under variable climatic conditions, maximising cane yield, farming profitability and the economic value of irrigation water. A working example is conducted in the sugarcane industry of the Burdekin district, Queensland, the largest irrigated cane-growing region in Australia. Our findings show that a more frequent irrigation schedule (Schedule 1) improved model-simulated potential cane yield and profitability by reducing water stress, without considering the extra cost of higher irrigation frequency. A consistent water supply enhances nutrient uptake and growth, resulting in higher potential yields (30 t ha−1 per season (14%)) and profitability (up to AUD 500 ha−1 per season) than those of a less frequent schedule (Schedule 2). Maximum economic water value (EWV) of AUD 258 ML−1 is achieved in a wet season due to enhanced moisture availability/air humidity and reduced irrigation demand, while better EWVs are achieved by ratoons in all seasonal climate conditions. An optimal irrigation schedule adapting to each seasonal climate condition is recommended for improved irrigation management. Overall, we recommend a 4-steps practical irrigation decision framework for each cropping season: (1) classify the wet/normal/dry upcoming season, (2) select specific optimal water amount (irrigation depth) and interval based on the present proposed method, (3) estimate the total seasonal irrigation water needed in comparison with water allocation/availability, and (4) compare the EWV with water market price to decide buying/selling.