On-farm emissions

Where do agricultural emissions come from?

Many gases created by human activities act as greenhouse gases. The three most important from a New Zealand agricultural perspective are methane, nitrous oxide, and carbon dioxide.

Methane

Biogenic methane, is generated by ruminants as a by-product of digestion with a small amount (5 per cent) coming from dung and effluent systems.

The total feed eaten by livestock on your farm (per kilogram of dry matter intake) is the key driver of methane emissions.

How methane is produced

Methane, which is mostly emitted when cows burp, is produced in the rumen of the cows by microbes. These microbes are naturally present in all ruminant animals.

The average dairy cow produces about 98kg of methane annually, with 95 per cent coming from digestion. New Zealand studies have shown that about 21-22 grams of methane are produced per kg of dry matter eaten.

Why is methane recognised differently?

Methane has a relatively short life of 12 years. After 12 years, 80 to 89 per cent of methane breakdowns into carbon dioxide and water, which is why it is considered a short-lived gas. Despite its short lifespan, methane has an intense warming effect. It is more than 25 times as potent as carbon dioxide at trapping heat in the atmosphere.

Long-lived gases such as carbon dioxide and nitrous oxide however continue to add additional warming to the atmosphere for hundreds of years.

The Zero Carbon Act 2019  recognises this difference and uses a spilt gas approach.

For further information on greenhouse gases visit Methane and other major greenhouse gases | Ministry for the Environment

Nitrous oxide

Nitrous oxide is the gas released into the atmosphere from dung, urine patches, and nitrogen (N) fertilisers.

The amount of nitrogen applied in a dairy system as well as the percentage of nitrogen in feed are the main drivers of nitrous oxide emissions. Temperature and soil moisture can also play a role.

How is nitrous oxide produced?

When animals graze nitrogen-rich pastures only a fraction of the nitrogen consumed supports the production of milk or meat. Most of it ends up excreted in urine and dung.

The loading rate of nitrogen in a urine patch can be up to 1000 kg N per ha

Nitrogen is released from the soil when urine, faeces and fertilisers are broken down by naturally occurring microbes in the soil.

Carbon dioxide

The main drivers of carbon dioxide emissions on farm are woodlots and energy from fossil fuels. Forests and woodlots capture (or sequester) carbon dioxide and release it when cleared. To a lesser extent, the application of lime and urea nitrogen fertilisers can also contribute to farm carbon dioxide emissions. Carbon capture (and release) through soil can also occur. This is under investigation so it can be better quantified.As carbon dioxide is already accounted for under the New Zealand Emissions Trading Scheme, it will not be included in your farm greenhouse gas emissions report.

How are emissions measured?

Agricultural emissions are recorded using production data from processors and Stats NZ Agricultural Production Survey.

Internationally the agreed metric for measuring emissions is GWP100. This metric creates one single figure for a country’s emissions to measure all greenhouse gases in a 'carbon dioxide equivalent' over 100 years.

GWP100 works well for carbon dioxide emissions as carbon dioxide stays in the atmosphere for thousands of years. However, it overstates the warming impact of methane emissions by three to four times when emissions are stable.

It is particularly important biogenic methane is measured and treated accurately in New Zealand because agriculture is a much larger proportion of our economy than other countries, and this is reflected in our emissions profile.

DairyNZ is advocating for appropriate metrics to measure and report on methane emissions, such as GWP*, which better reflect the warming impact of methane over time. Find out more about our work on warming science.

Gross greenhouse gas emissions in 2021 by sector sub-category

To view more about the dairy sector's emissions profile and how it compares to other sectors, visit Ministry for the Environments inventory page and climate tracker.

However, with respect to efficiency of production on the international stage, Kiwi dairy farmers have one of the world’s lowest carbon footprints.

AgResearch analysis commissioned by DairyNZ, shows New Zealand as the world’s lowest-emission dairy milk producer with an on-farm carbon footprint 46 percent less than the average of 18 countries studied.

The research analysed 55 percent of global milk production, including major milk producing countries.

Carbon footprint of milk production