Effects of management and technology scenarios on the carbon footprint of milk from pasture-based dairy farm systems.

Consumers are increasingly concerned with their environmental impacts, especially GHG emissions from food production. The main goal of this study was to scope the current and future mitigation practices that can be implemented for pasture-based dairy production, how their effect on emissions could differ by region and farm system and affect long- and short-lived gases differently. To do this, we estimated the total GHG emissions and carbon footprint of milk from New Zealand-average (total of 352 farms) and regional (Canterbury and Waikato) dairy farm systems that rely on grazed pastures for the year 2020 and a projection for 2040 using a cradle to farm-gate life cycle assessment approach. We also simulated a series of mitigation scenarios considering the potential effects of farm management changes and technologies available currently and in the future. For mitigations currently available, the most significant reductions (compared with the baseline 2020 data) occurred by changing the type of brought-in feeds, decreasing stocking rate, and changing manure management. Replacing brought-in feeds that have a high footprint (e.g., imported palm kernel expeller) with maize silage produced locally resulted in a reduction from 5.0% to 19.2% of the footprint (per kg fat and protein-corrected milk). Complete removal of N fertilizer had little effect on the carbon footprint of milk (-0.1% and -0.4%) but was associated with lower production of milk and lower per-hectare GHG emissions (by 9%-11%). The future mitigation that showed the largest potential reduction was the use of methane (CH) inhibitors for enteric CH (3-nitrooxypropanol [3NOP] scenario), which is a major source of GHG emissions for dairy grazing systems. This mitigation showed a large potential short-term and sustained decrease in CH but would lead to continued CO emissions from 3NOP production and use. Another important possible trade-off is that some mitigations resulted in lower total GHG emissions per farm but lower milk production per hectare. Under such circumstances, it is important to carefully consider unintended emissions that may arise as a result of management decisions to compensate for lower milk production per farm, such as land use change to increase the dairy area.