Climate change effects on pasture-based dairy systems in south-eastern Australia

Increases in temperature, along with possible decreases in rainfall, will influence the production of forage on Australian dairy farms. A biophysical simulation study was undertaken to compare the performance of perennial pastures and annual forage cropping systems under a historical scenario and two possible future climate scenarios for three key dairy locations of south-eastern Australia. Pastures and forage-cropping systems were simulated with the biophysical models DairyMod and APSIM, respectively, for a location with a heavy reliance on irrigation (Dookie, Victoria), a location with a partial reliance on irrigation (Elliott, Tasmania), and a dryland location (Terang, Victoria). The historical climate scenario (baseline scenario) had no augmentation to climate data and an atmospheric CO₂ concentration of 380 ppm, whereas the two future climate scenarios had either a 1 Celsius degree increase in temperatures (with an atmospheric CO₂ concentration of 435 ppm) and a concurrent 10% decrease in rainfall, or a 2 Celsius degree increase in temperatures (with an atmospheric CO₂ concentration of 535 ppm) and a concurrent 20% decrease in rainfall. At Dookie, mean annual dry matter yields of the forage-cropping options and the pasture systems increased under both future climate scenarios but more irrigation was required. At Terang, the yield of forage-cropping systems increased whereas the yield of the pasture systems decreased under the future climate scenarios. At Elliott, yields of irrigated pastures and cropping systems increased but there was minimal or a negative impact on yields of dryland pastures and cropping systems under the future climate scenarios. At all three locations, forage production increased in the colder months of the year with a decrease in production during the warmer months. This study indicates that double-cropping and irrigated-pasture systems at all three locations appear resilient to projected changes in climate; however, for irrigated systems this assumes a reliable supply of irrigation water. The systems implications of how a shift in the seasonality of forage supply within these options impacts on the farm system as a whole warrants further investigation.