A new calibration of the Australian Farm Optimisation (AFO) model has been developed to better represent mixed farming systems in Western Australia’s low rainfall zone.
The calibration is based on the Merredin region, where farms are predominantly cropping enterprises with an important livestock component. Average farms in the region are approximately 6,093 ha, with around 77% of the farm area cropped and 23% allocated to pasture and livestock.
A major focus of the calibration was representing the substantial variation between seasons. Historical weather records and APSIM crop simulations were used to develop a set of eight representative weather-years, based on early-season rainfall, the quality of the seasonal break, and winter–early spring rainfall. Together, these indicators explained 78% of the variation in simulated crop yield between years.
The calibration also captures differences between the major soil and land management units found in the Merredin region. Eight land management units are represented, allowing crop and pasture productivity to vary with soil type and seasonal conditions.
Crop production parameters were developed using regional benchmarking data, APSIM modelling and input from local agronomists. The model accounts for seasonal effects on yields, fertiliser and chemical use, as well as important rotational effects between crops and pastures.
Pasture production was calibrated using AusFarm simulations and validated against expert knowledge, satellite-derived pasture information and other modelling data. This allows AFO to represent changes in pasture growth, germination and feed quality across contrasting seasonal conditions.
Together, these inputs provide a regional representation of the biological and management conditions faced by mixed farms in the low rainfall zone. The calibration provides the foundation for using AFO to examine questions around farm profitability, crop–livestock integration and the future role of sheep in mixed farming systems.
For the full methodology, assumptions, data sources and calibration parameters, view the full AFO Low Rainfall Zone Calibration Report below.