Consequential Life Cycle Assessment of pasture-based milk production: a case study in the Waikato region, New Zealand

Farm intensification options in pasture-based dairy systems are generally associated with the use of increased stocking rates coupled with the use of off-farm inputs to support the additional feed demand of animals. However, as well as increasing milk production per hectare, intensification can also exacerbate adverse impacts on the environment. The objective of the present study was to investigate environmental trade-offs associated with potential intensification methods for pasture-based dairy farming systems in New Zealand. Methods: Multiple environmental impacts of potential farm intensification scenarios for pasture-based dairy systems in the Waikato region, New Zealand were modeled using Consequential Life Cycle Assessment. The intensification scenarios selected were (i) increased pasture utilization efficiency (PUE scenario), (ii) increased use of N fertilizer (urea) to boost extra pasture production (N fertilizer scenario), and (iii) increased use of brought-in feed as maize silage (MS) to support extra feed supply (MS scenario). Twelve impact categories were assessed and scaled to a functional unit of 1 kg extra fat and protein corrected milk: Climate Change (CC), Ozone Depletion Potential (ODP), Non-cancer effects (Non-cancer), Cancer effects (Cancer), Particulate Matter (PM), Ionizing Radiation (IR), Photochemical Ozone Formation Potential (POFP), Acidification Potential (AP), Terrestrial Eutrophication Potential (TEP), Freshwater Eutrophication Potential (FEP), Marine Eutrophication Potential (MEP) and Ecotoxicity for Aquatic Freshwater (Ecotox). Sensitivity analysis was carried out to test the effects of choice associated with (i) approaches to account for indirect land use change (ILUC) and (ii) competing (displaced) product systems (conventional beef systems) on the CC indicator for the three intensification scenarios. Results: The PUE scenario had 9 out of the 12 environmental indicators that were lowest. The exceptions were the IR indicator where the result was higher than the N fertilizer scenario result (but lower than the MS scenario result), and the AP and TEP indicators where they were slightly higher than the MS scenario results (but lower than the N fertilizer scenario results). For the MS scenario, 7 (ODP, Non-cancer, Cancer, IR, POFP, FEP and Ecotox) out of the 12 indicator results were higher than those for the N fertilizer scenario. For the N fertilizer scenario, 5 (CC, PM, AP, TEP and MEP) out of the 12 indicator results were higher than the results for the MS scenario. The magnitude of the CC indicator results was influenced by the ILUC accounting approaches and choice associated with a global marginal beef mix used to handle the co-product dairy meat, but the relativity of the CC indicator results for the three intensification scenarios remained unchanged. Discussion and conclusions: The PUE method is the environmentally preferred intensification method. In contrast, the preferred choice between the N fertilizer and MS methods depends upon trade-offs between different environmental impacts. These trade-offs require further modeling to transform them into a more understandable and interpretable indicator (or indicators) in order to facilitate comprehensive decision-making associated with environmental sustainability of the dairy sector.