B Cullen1, R Rawnsley2 and R Eckard1
1Melbourne School of Land and Environment, University of Melbourne, Australia
2Tasmanian Institute of Agricultural Research, University of Tasmania, Australia
Adapting pasture-based dairy systems to future climates.
Abstract
Australian pasture-based dairy systems rely on efficient conversion of pasture to milk, with
stocking rate and calving time being key management decisions used to align animal
requirements with the seasonal pattern of pasture supply. Pasture production is heavily reliant on
the climate, and projected climatic changes will alter the pattern of pasture growth requiring farm
managers to adapt their grazing systems. In south eastern Australia, climate changes for this
century indicate warming with a drying trend. The capacity to adapt stocking rate and calving time
to future climates was explored, by examining the impact of climate changes on pasture
production and farm gross margin at three sites; Terang (south-west Victoria, Mediterranean
climate); Ellinbank (Gippsland, Victoria, temperate climate); and Elliott (north-west Tasmania,
cool-temperate climate).
A baseline (1971-2000) and 20 future climate scenarios covering the range of climate projections
were examined at each site. Future climates were created by scaling the baseline climate by
warming of 1, 2, 3 and 4oC (with atmospheric CO2 concentrations of 435, 535, 640 and 750 ppm
respectively) and scaling rainfall events by -30,-20,-10, 0 or +10%. For each scenario, production
of perennial ryegrass/white clover pasture was simulated using DairyMod. Optimal stocking rate
and calving time for each scenario was determined by the highest average gross margin using
DairyPredict.
In the baseline climate, the mean annual pasture production was 10.7, 11.4 and 12.5 t DM/ha for
the Terang, Ellinbank and Elliott sites respectively, with corresponding farm gross margins of
$1336, $1538 and $2185/ha. The optimal management was 2.25 cows/ha calving in June at
Terang and Ellinbank, and 2.25 cows/ha calving in July at Elliott. Annual pasture production
declined with warming at Ellinbank and Terang, while at Elliott there was no difference in pasture
production between 2, 3 and 4oC warming which were greater than at 1oC warming. At Elliott
there was an increase in pasture production with +10% rainfall, but significantly lower production
with each 10% rainfall decline. At Ellinbank and Terang there was no difference in pasture
production between the 0 and ±10% rainfall change scenarios, while production declined with -20
and -30% rainfall.
Compared with using the baseline management, farm gross margins in the future climate
scenarios were improved when stocking rate and calving time were adapted to match the
changes in pasture supply. Where lower pasture production was modelled, reducing stocking rate
alleviated some of the reduced gross margin compared to maintaining the baseline management.
Where higher pasture production was simulated the implementation of higher stocking rates and
earlier calving increased gross margins.
The mean benefit of adapting calving pattern and stocking rate, compared to maintaining the
baseline management, across all future climate scenarios was $76, $58 and $471/ha at Terang,
Ellinbank and Elliott respectively, indicating larger benefits in the cool temperate region where
pasture production was expected to increase in a warmer climate. Consistently lower gross
margins and smaller benefits of adaptation were simulated in the Mediterranean and temperate
regions suggesting that further changes to the farm system are required to maintain profitability.