A national study of the effectiveness and co-benefits from actions to mitigate water quality impairment and greenhouse gas emissions from dairy farms in New Zealand

CONTEXT Many jurisdictions have policies that require simultaneous reductions in greenhouse gas (GHG) emissions and nitrogen (N) and phosphorus (P) losses to water. In New Zealand's pasture-based dairy sector, farm planning tools are used to target actions to mitigate emissions and nutrient losses. However, the regional effectiveness and co-benefits from these actions are highly variable. OBJECTIVE We aimed to determine if widely promoted on farm actions, implemented independently, could reduce emissions and nutrient losses with minimal trade-offs, and if effectiveness would vary by region. METHODS Using data from over 750 dairy farms (2013–2024) and > 6300 data records in New Zealand, we used gradient boosted regression trees to model changes in emissions and losses in response to six mitigation actions: three examined reduced fertiliser usage options, two improved irrigation and effluent practices, and one avoided winter forage cropping. RESULTS AND CONCLUSIONS Modelling indicated reductions in N and P losses to water (0–21% and 1–10%, respectively) and GHG emissions (1–11%) with no statistically significant trade-offs between water and air outcomes. Avoiding winter forage cropping substantially reduced N and P losses in regions where the practice is prevalent. The greatest overall benefits were observed in Canterbury and Southland. Results demonstrate that widely promoted good farming practices can deliver simultaneous improvements in water quality and climate performance. SIGNIFICANCE This study provides national-scale evidence to support ongoing good farming practice implementation and give farmers confidence that multiple environmental outcomes can be pursued with minimal unintended consequences, while highlighting that the extent and feasibility of uptake will depend on individual farm systems and local conditions.