Agriculture accounts for 49.2% of gross Greenhouse gas (GHG) emissions in New Zealand (NZ). Methane from enteric fermentation makes up 37% of New Zealand's gross emissions, with dairy cattle contributing significantly at 22.7% [1]. In the last three decades, there has been significant increases in both dairy cow numbers and synthetic nitrogen fertiliser use in the Canterbury region. In 1992 there were 50,000 dairy cows in Canterbury and 3.2kT nitrogen fertiliser used on dairy farms, in 2019 there were 1.2m dairy cows (including milking cows and dry cows) and 57kT of nitrogen fertiliser was used. The Canterbury dairy agriculture system must urgently reduce it’s GHG emissions in line with the 1.5ºC failure limit for global warming carbon while staying within environmental limits and continuing to provide nutrition for growing global population.

This thesis explores opportunities to decarbonise dairy agriculture in Canterbury. It couples transition engineering methods with farm system modeling to evaluate the performance of theoretical farm systems with a variety of GHG mitigation strategies in place. Defining the essential activity of the Canterbury agriculture sector as providing nutrition, rather than necessarily producing milk solids allows us to explore scenarios where dairy production is downshifted and nutrients are provided by alternative food crops.

The paper begins with a review of literature related to greenhouse gas mitigation strategies in global agriculture and New Zealand dairy agriculture, farm system modeling, regulation of NZ agriculture and environmental harms associated with dairy farming. Chapter 3 describes how transition engineering methods were used to aid with problem definition and development of research objectives. Chapter 4 characterises the present-day Canterbury dairy agriculture system in terms of production, financial performance and environmental performance. Chapter 5 presents a brief history of dairy agriculture in Canterbury. Chapter 6 describes scenario selection, farm system modeling results. Chapter 7 explores opportunities to transition to a low emissions Canterbury agriculture sector. Finally, the paper ends in Chapter 8 with final conclusions and recommendations for further research.

The results suggest that there is no technology solution that achieves the deep emissions reduction required without decreasing dairy production. There will need to be a significant reduction of the dairy herd in Canterbury, coupled with increased production of plant-based protein sources. Synthetic nitrogen fertiliser must also be significantly reduced, along with an increase organic farming and other practices that improve soil health, biodiversity and ecological outcomes. Increasing production of plant based crops significantly increases food production per hectare and significantly decreases GHG emissions both in terms of perhectare of farm area and food production but with a significant decrease in profitability. The most profitable wheat scenario was organic wheat with electrified farm vehicles, and transport. With a carbon price of $165.40 the Organic and Electric Wheat scenario becomes as profitable as the business as usual (BAU) scenario with a high proportion of palm kernel extract purchased as supplementary feed. An organic mixed farm system where cow numbers are reduced by 75% decrease emissions by 74%, with only a 25% reduction in profitability compared with the BAU scenario.