Pressure on livestock eases a little

Cows, it seems, aren't doing quite as much environmental damage as they have been accused of. Picture / File

DairyNZ has welcomed news that New Zealand's greenhouse gas inventory has been updated to reflect new science on nitrous oxide emissions, which showed that dairy cows and other livestock produce less emissions than previously estimated.

New Zealand's Greenhouse Gas Inventory is the official annual estimate of all human-generated greenhouse gas emissions, the most recent inventory, for the period from 1990 to 2018, incorporating new research on livestock emissions on different land gradients.

AgResearch and Manaaki Whenua scientists have carried out research on livestock emissions for more than a decade, finding that on rolling and steep hill country, nitrous oxide emissions from urine is lower, as a result of factors related to soil composition and topography. Emissions for dairy cattle on flat land were also recalculated to be slightly lower as a result of their research.

While the impact of the changes for 2017 was modest, with total dairy cattle emissions being 1.4 per cent lower than previously estimated for that year, DairyNZ strategy and investment leader Dr David Burger said the research was important.

"We now have more accurate estimations of livestock emissions on sloping land," Dr Burger said.

"The current inventory calculations assume almost all dairy cattle are located on flat land, but we know that cows are often grazed on rolling land, particularly when they are young or during winter.

"Once we have more data on the proportion of dairy cattle on sloping pastures, we will have a more accurate understanding of emissions, which may see dairy nitrous oxide emissions change further."

As part of the Dairy Tomorrow strategy, dairy farmers had committed to protecting and nurturing the environment for future generations, he added, that commitment including work to lead efforts to meet New Zealand's climate change goals through identifying and implementing strategies to reduce or offset greenhouse gas emissions on dairy farms.

Under a 2019 partnership agreement (He waka eke noa) between the government and primary sector organisations, all farmers would work to have Farm Environment Plans by 2025, setting out how good farming practices would help to manage emissions.

Since 2017, the number of milking dairy cows in New Zealand has remained relatively stable (4.85 million in 2016/17 and 4.95 million in 2018/19).

Meanwhile Federated Farmers spokesman Andrew Hoggard said the finding underlined the value of in-depth research and accurate data, and the federation thanked the researchers at AgResearch and Landcare Research, and the officials at MPI, who continued to work hard to improve the accuracy of the national Greenhouse Gas Inventory.

Mr Hoggard said Federated Farmers supported the 2050 nett-zero N2O target that was recently added to the Climate Change Response Act, requiring the livestock industry to either reduce or offset the approximately 8700 kilotonnes of CO2- e (carbon dioxide equivalent ) of nitrous oxide that were emitted in 2017 (the most recent year data was available for) by 2050.

That would not be easy to do, but it was a task that farmers were committed to.

"The difficulty in reducing nitrous oxide is due to the emissions being mainly caused by the urine of livestock providing too much nitrogen for the soil to absorb," Mr Hoggard said.

"While nitrogen is good for plant growth, when there is too much nitrogen in one spot, some will be released into the air as nitrous oxide."

The "absurd impracticality" of measuring the emissions caused by the urine of individual livestock on-farm meant that totals were estimated using models and the best scientific research on hand, however. Unlike a factory, there was no device to directly measure the emissions from animals on farms, so it was a case of attempting to estimate complex biological process as best as possible.

The new research showed that urine deposited by livestock on hilly terrain spread over a larger area, and was therefore better absorbed by the soil. That, coupled with the distinct microbial makeup of hill soil, resulted in less nitrogen being lost to the atmosphere as nitrous oxide emissions.

Rather than representing a decrease in N2O emissions for this year, however, the research showed that New Zealand's nitrous oxide emissions had been overestimated since the keeping of records began in 1990.

"The new research results in a 1700kt CO2-e reduction in agricultural nitrous oxide emissions estimated for 2017, an almost 20 per cent reduction," Mr Hoggard said.

"The bulk of these reductions come from sheep and beef livestock on steep slopes, but a lack of data resulted in the assumption being made that all dairy cattle are located entirely on flat terrain. We encourage the researchers and officials to continue to work with the agriculture industry in New Zealand in order to also make this innovative research applicable to dairy farmers."

The research resulted in hill country sheep and beef nitrous oxide emissions being reduced by about two-thirds and one-third respectively in the emissions inventory back to 1990.

"Farmers across New Zealand are committed to improving environmental outcomes at home, while continuing to provide sought-after and nutrition-packed food across the globe," he added.

"This research highlights the fundamental importance of accurate data in managing environmental outcomes, such as greenhouse gas emissions. New Zealand is at the cutting edge of agricultural climate change research, and Federated Farmers encourages researchers and officials to continue their hard work towards more accurately understanding the wicked problem of climate change that is facing farmers, along with all New Zealanders."