Simulating the efficiency and resilience of diverse crop sequences in Australia’s subtropical cropping zone

Farming systems in Australia’s subtropics have been under-performing. This study used simulation modelling to evaluate common crop sequences used in subtropical Australia in terms of their system water-use-efficiency (WUE) and resilience to climate variability. The analysis here examines this for 4 locations spanning the subtropical farming systems of eastern Australia. We found significant variation in the system WUE ($/ha/mm) amongst crop sequences, with common crop sequences in each location found to be 12-40% less WUE than the best crop sequence. Cropping intensity is a key driver of system profitability and risk, more so than a mix of crops used. Crop systems with higher intensities (i.e. less time in fallow) have higher average profitability but also higher risk; conversely, crop systems with longer fallows have a lower risk but there are trade-offs of lower long-term gross margins. It is critical to match cropping intensity to the environment to optimise the risk-return trade-offs. Lower crop intensities (0.5-0.75 crops/yr) are optimal in harsher environments (e.g. western districts), moderate crop intensities (0.75-1.0 crops/yr) in the moderate environments, but crop systems with higher crop intensities (1.0-1.3 crops/yr) are optimal in higher rainfall environments.