Management and production factors that determine greenhouse gas emissions in heterogeneous dairy farms in New Zealand

The New Zealand dairy industry accounts for approximately 25% of national greenhouse gas (GHG) emissions. Dairy farms are heterogeneous in their management and production characteristics, resulting in varying emissions across farms. This variability in emissions leads to diverse abatement costs and GHG mitigation potential. This study aimed to explore farm heterogeneity in GHG emissions and identify key management and production factors associated with emissions and operating profits across New Zealand’s dairy farms. Unbalanced longitudinal panel data from DairyBase spanning 10 consecutive milking seasons (2012-13 to 2021-22) were used. Pearson correlation analysis was used to examine associations among GHG emissions, farm management and production indicators. Linear mixed-effects regression model was then applied to estimate the effects of key management and production factors on emissions and operating profits. The results revealed regional heterogeneity in farm characteristics and emissions across dairy farms. Total GHG emissions showed an overall increasing trend over the study period, with year-to-year fluctuations. GHG emissions per hectare showed strong positive associations with key production indicators, including milk solids production per hectare ( r = 0.82), total feed intake per hectare ( r = 0.76), pasture and crop intake ( r = 0.75), and stocking rate ( r = 0.72). Total feed intake, nitrogen fertilizer application, and irrigation showed significant positive effects on both emissions and operating profits. Transitioning from twice-a-day to lower milking frequency showed reduced emissions but mixed results for operating profit. The findings highlight that reduced use of nitrogen fertilizer and supplementary feeds corresponded with reduced emissions but also with reduced farm profits. Given the diversity in farm characteristics and emissions across dairy farms, further investigation through farm-level classification is needed to identify effective farm-specific GHG mitigation options.