Life cycle environmental impacts of high and low intensification pasture-based milk production systems: a case study of the Waikato region, New Zealand.

Intensification of pasture-based dairy farming systems is usually associated with increased use of off-farm inputs to increase milk production per hectare, and additional environmental impacts may be associated with upstream production and delivery of these off-farm inputs. The objective of this study was to compare two levels of dairy farming intensification (i.e. high versus low) in pasture-based milk production systems with respect to (i) farm production and (ii) life cycle environmental indicators. The study considered 53 dairy farms in the Waikato region, New Zealand. Three farm attributes (stocking rate, amount of brought-in feeds and amount of nitrogen fertilizer used) were used to define a level of farming intensification (Intensification Index) for each dairy farm. The upper and lower quartiles of the dairy farms ranked on their Intensification Indices were chosen to represent high and low intensification groups, respectively. Twelve midpoint environmental indicators of the dairy systems were assessed using attributional Life Cycle Assessment with one kg of fat- and protein-corrected milk as a functional unit and a cradle-to-farm gate perspective as a system boundary. Compared with the low intensification group, the high intensification group had (on a per hectare basis) higher (P < 0.001) stocking rate, total brought-in feeds and nitrogen fertilizer use, which led to greater milk yield per cow (P < 0.01) and per hectare (P < 0.001). The different levels of farming intensification did not affect total feed conversion efficiency (P > 0.05). However, for the high intensification group, the results for 10 out of 12 environmental indicators per kg of fat- and protein-corrected milk were higher (P < 0.05) than those in the low intensification group. The main drivers for the increases in most environmental indicator results were the production of brought-in feeds, manufacturing of agrichemicals and transportation of off-farm inputs for use on dairy farms. In contrast, increased pasture intake was negatively correlated (P < 0.05) with all environmental impacts, indicating that efficient pasture management is also critical to mitigate environmental impacts. In conclusion, while an increase in intensification of pasture-based dairy farming systems led to increased milk production per cow and per hectare, it also resulted in increased environmental impacts for most indicators. Apart from increased resource use efficiency, increased pasture utilization efficiency is a promising measure to improve environmental sustainability of pasture-based dairy farming systems.