Mitigating greenhouse gas emissions in Australian dairy farming: A modeling approach to evaluating stacking of current and emerging strategies.

The dairy industry faces increasing pressure to reduce greenhouse gas (GHG) emissions in response to environmental and regulatory requirements. This study investigated the potential for GHG reductions on Australian pasture-based dairy farms by evaluating current and emerging strategies using 3 case studies. Data were collected and used in the Dairy Greenhouse Gas Accounting Framework. Mitigation strategies already available to farmers, such as 3-nitrooxypropanol supplementation, enhanced-efficiency fertilizers, and tree planting, were modeled alongside emerging options, including selective breeding, chemical treatment of effluent ponds using polyferric sulfate and sulfuric acid (EcoPond technology), and high-tannin white clover pasture. This study also modeled a practical timeline for the adoption of these strategies and integration into farm systems. The baseline total annual emissions (Scope 1+2+3) of farms in Gippsland, Northern Victoria, and Bega were 4,627, 2,970, and 3,492 t CO2e, respectively. Baseline emissions were dominated by enteric methane, representing 55-58% of total farm emissions, followed by manure management (12-15%). Carbon sequestration from existing vegetation offsets was less than 3.5% of emissions for each farm. The results demonstrate that stacking mitigation strategies can lead to considerable reductions in net GHG emissions, with maximum reductions (per year) achieved 18 years after implementation for Gippsland farm (72% by 2043), 14 years for Northern Victoria farm (52% by 2039), and 15 years for Bega farm (46% by 2040). Among the strategies used, tree planting provided the greatest contribution to net emission reductions, with sequestration from trees offsetting 45%, 22%, and 18% of total farm GHG emissions at the peak year of reduction for the Gippsland, Northern Victoria, and Bega farms, respectively. Despite the benefit of tree planting, its large-scale implementation on dairy lands may reduce productivity, highlighting the need for a balanced approach. While the gradual integration of these strategies offers a feasible pathway to achieving long-term reductions in emissions in dairy farming, the time required for full implementation may limit the potential for achieving short-term emission reduction targets.