Opportunities to improve sustainability on commercial pasture-based dairy farms by assessing environmental impact25 October 2018
For pasture-based dairy farming to become more sustainable, the negative environmental impacts associated with milk production must be minimized. These negative impacts include eutrophication, ammonia emissions and greenhouse gas (GHG) emissions. Two tools, a nutrient budget and a carbon footprint calculator, allow farm-level assessments of these negative impacts. In this study, a nutrient budget was used to calculate the efficiency of nitrogen and phosphorous use, and a carbon footprint calculator was used to calculate GHG emissions. Farm system descriptors were used to identify the farm systems that had the lowest environmental impact. Soil carbon was measured as an indicator of soil health, and the link between soil health, nutrient use efficiency and GHG emissions was examined. Nitrogen and phosphorous were not efficiently utilized on the farms included in this study, with a large excess of nutrients imported onto the farms each year. The average use efficiency was 29% for nitrogen, and 36% for phosphorous. The GHG emissions per liter of milk production were higher on the farms included in this study than found in previous studies on dairy farms, with an average of 1.39 kg of carbon dioxide equivalents emitted per kilogram of energy-corrected milk. Farm systems which optimized milk production on the available land, while applying the least amount of fertilizer and feeding the least amount of purchased feeds per milk produced, had the lowest environmental impact. Farms with higher soil carbon levels had higher nitrogen use efficiencies and lower GHG emissions. This is the first South African research to examine environmental impact on pasture-based dairy farms in this manner. It is possible for pasture-based dairy farmers to reduce the environmental impact of milk production by adopting some of the principles identified in this study.