The American industry has set a goal of 25% reduction in greenhouse gas emissions by 2020.
The interdisciplinary team in Arkansas is examining all facets and stages of milk production, from the fertiliser used to grow feed to packaging disposal after consumer use. For every kilogram of milk consumed in the US each year 2.05kg of greenhouse gases, on average, are emitted over the entire supply chain.
Feed production accounts for 20%; on-farm emissions account for 53%; processing accounts for 12%; retail channels account for 10%; and consumption and disposal account for 6% of the national global warming potential for the consumed milk.
Stewart Ledgard, principal scientist in the land and environment group at AgResearch, highlighted the finding that about one-third more milk needs to be produced relative to the actual amount consumed. The losses are based on US Department of Agriculture (USDA) food loss reports.
The greenhouse gases were measured as carbon dioxide equivalents and included methane, refrigerants, and other gases that trap radiation. The largest contributors were feed production, enteric methane, gas emitted by the animal itself, and manure management.
Several areas where the industry can reduce the impact have been identified. The researchers focused on farms, where processes for feed production, handling of enteric methane and manure management varied greatly. They represented the greatest opportunities for achieving reductions.
They suggested strategies that linked inorganic fertiliser use with applying manure for crop production. They recommended dry lot and solid storage systems, rather than anaerobic lagoons and deep bedding. Methane digesters, which convert manure to methane for energy, are recommended for larger farm operations.
At the processor and distribution level, greater emphasis on truck fleet fuel usage and electricity consumption would reduce emissions, the researchers said.
Implementing standard energy-efficiency practices for refrigeration and compressed-air systems, motors and lighting would also lead to reductions. Processor plant fuel reductions could be achieved through improved steam. In the packaging phase, emissions reductions could come from improved bottle designs resulting in less material use.
The researchers recommended a careful examination of trucking transport distances to realise greater optimisation and efficiency of routes. They also suggested transport refrigeration systems that use fewer refrigerants.
Ledgard and other New Zealand scientists are not surprised that the Americans found the largest contributors to greenhouse gases were feed production, enteric methane and manure management. For the farm stage, the American researchers estimated 1.23kg CO2equiv/kg fat-and-protein-corrected-milk for an average US farm, whereas the published work in NZ showed an average of 1kg.
“However, there will be some methodology differences,” Ledgard said.
Like the US work, NZ studies have shown there is large variability between individual farms. Ledgard said the US study was one of the few, and maybe only, for milk that looked across the whole of the lifecycle. AgResearch research for Fonterra looked only at farm, processing and transportation.
Most greenhouse gases in the US nevertheless came from the farm and, as in NZ, methane and manure nitrous oxide were dominant sources. The much greater use of housed systems in the US meant the Americans could get more benefit from practices such as methane digestion, Ledgard said.
NZ scientists had also identified efficient fertiliser use, especially nitrogen, as important.
In terms of retail, consumption and waste, NZ’s work with lamb and beef had highlighted similar areas where efficiencies could be made. Some of these could be seen as more applicable to milk, such as the potential benefits from improved packaging.
Legard said new work underway in NZ included a project looking at the effects of dairy intensification, especially the effects of different feeds.
Sarah McLaren, director of the NZ Life Cycle Management Centre and Associate Professor in Life Cycle Management at Massey University, said while carbon footprint work was continuing, the focus had shifted on to reducing the carbon footprint. This work was being done through the NZ Agricultural Greenhouse Gas Research Centre.
Headquartered at the AgResearch Grasslands campus in Palmerston North, the centre funds scientific studies by researchers working in their own organisations. Dr Harry Clark, the centre’s
director, said it was working on how methane nitrous oxide, in particular, could be reduced. This would help to reduce the dairy industry’s carbon footprint.
“There is a lot of work going on around mitigation,” he said.
“The carbon footprint tells you where you are but if you want to lower it you have to take action.”
