Eco-efficiency of intensification scenarios for milk production in New Zealand

New Zealand (NZ) dairy farms used to be the lowest input and most efficient dairy farms of the world. However, intensification of the traditional pasture-based system has occurred over the last decade and has not always been accompanied by increased efficiency. The purpose of this paper is to produce an updated reference of the eco-efficiency of NZ dairy farm systems and to analyse the implications of intensification on their eco-efficiency. Results for an average NZ dairy farm system were compared with those for three dairy farmlet systems representing a wide range in intensification practices. A low input system (LI) (no N fertiliser, no brought-in feed supplement, stocking rate of 2.3 cows/ha) was compared with an N-fertilised farm system (NF) (170 kg fertiliser-N/ha/year, 3 cows/ha) representing a first level of intensification and with an N-fertilised and maize silage supplemented system (NFMS) (170 kg fertiliser-N/ha/year, 13 t DM maize silage/ha/year, 5.2 cows/ha), representing a possible future intensification option. Their eco-efficiency in terms of milk production and land use was compared using Life Cycle Assessment (LCA) methodology. NZ dairy farm systems rely on favourable temperate climate conditions and long-term perennial ryegrass/white clover pasture, to achieve eco-efficient milk production and land use compared to European systems. However, intensification of NZ dairy farms was shown to be detrimental to their eco-efficiency in terms both of milk production and land use functions and could greatly reduce their advantage compared to European systems. The ecoefficiency of LI was very high whatever the functional unit which is remarkable from an LCA perspective. NF and NFMS had a similar eco-efficiency except for energy use which corresponded to the most critical hot spot of NFMS. All studied NZ systems presented some areas for improvement where some new technologies available for dairy farms might play a promising role in the future. Finally, it should be highlighted that the comparison with European studies based on the literature available needs validation through a more comprehensive study using harmonised methodology and assumptions across countries. (Résumé d'auteur