Increasing soil fertility and altering legume-grass balance as adaptation strategies for sustainable livestock production under climate change

Climate change is predicted to cause reduction of the annual primary productivity in grasslands across southern Australia. Elevated atmospheric CO2 concentrations are likely to favour legumes over grasses in temperate pastures, but legume residues have weaker structure compared to grass species. As a result, more rapidly degradable ground cover during summer can potentially increase risk of soil erosion. Managing pastures for lower legume content may prevent this issue as an adaptation option but at the cost of reduced production per animal. We applied the GRAZPLAN modelling tools to simulate potential effects of future projected climates (SRES A2 scenario) on pasture and livestock production of 24 representative livestock farms in southern Australia running five livestock enterprises. We applied historical weather data for 1970 to 1999 (as reference) and projected data from four global circulation models. Pasture and animal production were simulated for focus years at 2030, 2050 and 2070. At each location, and for each climate, we estimated the sustainable stocking rate with the current pasture composition (legume-grass mixture) and with legumes other than lucerne removed from the pastures. Increased soil fertility was also simulated as an adaptation option. At all examined locations, the legume removal option decreased the profit ($/ha) in comparison with the no adaptation option. Even applying the legume removal in association with the increased soil fertility could not make significant change from the no-adaptation case. Applying the single adaptation of increased soil fertility could partly recover decline in profitability of the farm systems, however its effectiveness decreased over time