According to the peer-reviewed study, ditching imported palm kernel and reducing fertiliser use would be a good start.
The research, published recently in the Journal of Dairy Science, estimated the emissions created by producing a kilogram of milk. The paper compared the carbon intensity of both different farms and different years.
Compared with estimates from other countries, New Zealand’s milk is “right at the bottom end” of carbon intensity, AgResearch principal scientist Stewart Ledgard said.
Although other countries tend to house animals indoors and ship in feed, Kiwi dairy cows typically get most of their energy from grazing pasture. “We’re not using a lot of fossil energy by cutting crops, harvesting them, storing them, bringing them in and feeding to animals.”
The research calculated all the emissions produced before the milk left the farm, but did not include the greenhouse gas emitted in the processing (such as milk drying) and transportation of the final product.
Each year, our agricultural sector emits the equivalent of 37.7 million tonnes of carbon dioxide (farming-related gases such as methane are more potent, but shorter-lived, than carbon dioxide, so the government averages each gas’ impact over 100 years and converts each tonne to a carbon dioxide-equivalent). That’s nearly 48 per cent of the country’s total.
Ledgard said supplementary feed – what’s brought in when pastures run low – is key. Low-carbon farmers both manage their fields to reduce the need for additional food but also choose low-emissions feed when they can’t avoid it.
Farmers could shave five per cent off their emissions footprint by choosing greener feeds, such as waste fruit and vegetables or locally grown maize, the paper found.
The cheapest and most common added feed on farms, imported palm kernel, was the most emissions-intensive.
“It comes out of Southeast Asia, so there are quite high emissions from the production of it, including deforestation in the area, plus it’s got to be put on a ship and carted to New Zealand,” Ledgard said. “The choice can have quite an effect on the emissions, particularly those farms that use moderate to higher amounts of those types of feeds.”
However, Nick Tait of Dairy NZ warned that phasing out imported palm kernel was “hard to do at this moment” based on the current availability of alternative feeds.
Federated Farmers president Andrew Hoggard said the drought conditions requiring farmers to increase supplementary foods can also affect locally grown crops, such as maize.
Farmers had to choose additional feed carefully as some (such as turnips) can taint milk and cost farmers financially, he said. “You can’t just go for anything and everything… [you] need to make sure feeds aren’t going to change the composition of the milk.”
The efficient use of nitrogen-based fertiliser – which creates the greenhouse gas nitrous oxide – is another important practice impacting the carbon intensity of milk. Ledgard said nitrogen fertiliser use has plateaued in recent years.
Our higher-carbon farms used almost 40 per cent more nitrogen fertiliser than lower-carbon ones, he said. “There is quite a lot of emissions associated with fertiliser production as well as from when the fertiliser goes on to land.”
The government’s recently announced freshwater protections, which include a cap on fertiliser use, are expected to reduce the country’s emissions.
Lower-emissions farming doesn’t require farmers to take an economic hit, Ledgard said. “[Farms] with the lowest carbon footprint, the most efficient ones, also had higher profitability.”
A combination of drought and high milk prices was a recipe for increased emissions, the research suggests. When the two occurred in Taranaki in 2017/18, farmers used additional fertiliser and shipped in extra feed to extend their milk production, which raised the carbon footprint of their milk.
The research paper found some climates, including Northland, have higher-carbon milk, no matter the year. Northland farmers use similar amounts of fertiliser to other regions, but get less bang for buck.
Dairy NZ was trying to help farmers to manage their pastures, supplementary feed and fertilisers efficiently, Tait said.
“There are benefits for water quality, emissions and profitability – you’ve got to look at it all together,” he said. “It’s coming on to a lot of farmers’ radars [though] there’s still a lot of work to do.”
Ledgard said the research found the carbon footprint of milk remained relatively stable in different years. There was a slight downward trend – which could be explained by the 2010/11 season’s widespread drought.
“The variation between the years wasn’t as great as I was perhaps expecting,” he said.
The research found, on average, 0.81kg of carbon dioxide was produced for each kilogram of milk in the 2010/11 season, compared to 0.75kg of carbon dioxide in the 2013/14 season and 0.78kg of carbon dioxide during the 2017/18 season.
Two international studies – published in 2014 – out of Australia and Ireland calculated 1.1kg of carbon dioxide was emitted for each kilogram of finished milk.
If total animal numbers don’t increase, practices lowering the carbon footprint of a kilogram of milk could lead to a reduction in New Zealand’s total emissions.
Ledgard said a cost on emissions could incentivise these practices. Currently, farms are due to face an emissions price on 5 per cent of their greenhouse gases in 2025.
Tait said the difference in carbon footprints between the most and least efficient farms was often wider overseas. “It’s a small window compared to other countries,” he said.
He noted the per-kilogram carbon footprint of milk used in the study was different to the total greenhouse emissions used in reports such as the Ministry for the Environment’s annual count.
