Modelling the responses of perennial ryegrass and a sub-tropical pasture species to future climate scenarios in Tasmania

Production and consumption of high quality pastures underpin the competitiveness of the Tasmanian dairy and pastoral industries. Climate change projections for Tasmania, sourced from the Climate Futures for Tasmania project, were used to assess the impacts of a changing climate on aspects of pasture production across Tasmania. The fine resolution (0.1° grid) of the dynamical downscaled model outputs allows for changes in climate, and therefore impacts, to be differentiated across the agricultural regions of Tasmania over the period 1971-2100. Under the A2 emission scenario, Tasmania is projected to experience a rise in mean temperatures of 2.6 to 3.3°C from the baseline period (1971–2000) to 2085 (2071–2100). Mean annual rainfall across Tasmania from the baseline to 2085 is projected to remain relatively unchanged. The biophysical model DairyMod was used to simulate the growth of perennial ryegrass (Lolium perenne L.) in a monoculture and in a mixture with a sub-tropical summer-active pasture species, under rainfed and irrigated conditions at four sites across Tasmania. The four sites represented the dairying and pastoral regions of the north-west (Flowerdale), the northern Midlands (Cressy), the north-east (Ringarooma) and the south (Ouse). The simulations were nutrient non-limited and identical soil physical and chemical parameters were used for each site. By 2085, perennial ryegrass yields under rainfed conditions are projected to increase above the baseline by 81% at Ringarooma and 137% at Ouse. However, greater yields (99% and 171% respectively) are projected with the adaptation option of including a sub-tropical pasture species in the sward. Annual irrigated perennial ryegrass yields are projected to increase at Flowerdale and Cressy until mid-century, then decrease by 2085 as a result of increasing daily maximum temperatures. With the addition of the sub-tropical pasture species at these sites, an increase in mean pasture yields is projected (35% and 46% respectively).