Managing greenhouse gas emissions in two major dairy regions of New Zealand: A system-level evaluation

New Zealand dairy farms are responsible for a large proportion of this nation's greenhouse gas emissions (GHG-e), arising mainly from enteric methane and urinary nitrogen deposition on pasture. De-intensification and the use of specific mitigation strategies can reduce GHG-e from dairy farms, but are generally costly. In this study, a farm-level model is used to analyse the cost of GHG-e mitigation strategies in medium- (10-20% imported feed) and high-input (20-40% imported feed) systems in the two major dairy regions of New Zealand (Waikato and Canterbury). Production intensity is measured solely in terms of feed importation, in accordance with standard practice in this nation. The focus of the study is to assess the cost-effectiveness of a variety of de-intensification and mitigation strategies aimed at reducing the negative impact of emissions constraints (reductions of 10, 20, and 30%) on farm profit. De-intensification options include changes in stocking rate, nitrogen fertiliser application, and supplement quantity. Mitigation options include feeding crops, improved reproductive management, use of feed pads, use of stand-off pads, and use of nitrification inhibitors. The model showed that a combination of reduced N fertiliser application and lower stocking rates were the larger changes experienced in the systems studied when GHG-e reductions were introduced. Nitrification inhibitors were only useful for mitigation once the GHG-e reductions required were so stringent that their cost was warranted to offset the significant costs associated with de-intensification in the high-input systems. Stand-off and feed pads were too expensive to warrant their use when not already available. Overall, de-intensification of the farming system proved to be more profitable than the use of specific mitigation practices when reduction of GHG-e was required. Maintaining a given intake of imported feed reduces the degree to which de-intensification may be used for abatement, thus inflating the cost of mitigation strategies on high-input farms.