Reduce nitrous oxide emissions

Nitrous oxide is a tiny component of the atmosphere but a potent and long-lived greenhouse gas.

It accounts for 12% of New Zealand's total greenhouse gas emissions. Most nitrous oxide emissions arise from agriculture. The Government has set a target of reducing nitrous oxide emissions to net zero by 2050, meaning on-farm action is critical.

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In this short video, Dr Cecile de Klein of AgResearch explains where nitrous oxide comes from, its effect on the atmosphere, and some of the options researchers are exploring that farmers and growers might be able to use to reduce their nitrous oxide emissions.

Transcript

Duration: 5:15

CARRIE GREEN:
Most NZ farmers are in the business of growing plants.

either to feed livestock or people, or produce seeds.

Applying nitrogen helps plants to grow.

But it's no secret that too much nitrogen can lead to nitrates entering our streams, rivers and lakes.

What you might not know is that nitrogen in the soil also produces a greenhouse gas that's far more potent than carbon dioxide or methane.

In a moment we'll show you what you can do to reduce emissions of this gas, But first let's see what's going on in the soil.


CECILE DE KLEIN:
There's no 'Planet B', this is what we've got and we need to leave it in a better place for our children and our children's, children's children.

So that they can enjoy life as we know it. That's really what drives me.

I've been working on nirous oxide emissions for over thirty years now.

It's a very potent greenhouse gas, it's about 300 times more effective at trapping heat than carbon dioxide

It's also a long lived gas. It stays in the atmosphere for over 100 years. But its warming effect can stay on for centuries after that.

Nitrous oxide is a gas that's produced naturally in the soil by microbes.

They use nitrogen that is in the system to convert to nitrous oxide.

Nitrogen gets introduced into farming systems through fertiliser, clover, supplementary feed and animal urine.

Soil microbes use that nitrogen that's in the soil to transfer it into a form that plants can use.

But not all of the nitrogen is used by plants. Some of it sits in the soil, mainly as nitrate.

And that can then leach into the waterways or convert into nitrous oxide.

So, tonne for tonne nitrous oxide is many times more effective at trapping heat than carbon dioxide.

Fortunately we produce a lot less of it. But nitrous oxide still accounts for around 12% of NZ's total greenhouse gas emissions.

There must be something we can do about it right? Let's see what the scientists are up to.

Some of the solutions they're looking into are using different plants to utilise the excess nitrogen in the soil.

And there are some new technologies on the horizon.

One example is looking at some new nitrification inhibitors that can reduce nitrous oxide emissions.

Using plantain also appears to hold some promise for reducing both nitrate leaching and nitrous oxide emissions.

Partly that's because there's less nitrogen going through the animal and there's less nitrogen in the urine.

But there also seems to be a positive effect of the plant roots on the soil microbes that will reduce nitrous oxide emissions.

Work is still ongoing and we still need to understand the mechanism behind this.

And also how plantain can be used best and how can we maintain it in the system. They're all big questions still to be answered.

So a number of solutions are showing real promise, but there are things you can try on your farm now that might make a difference. Let's take a look.

Key things to do are to consider whether you can reduce your fertiliser input.

There are more and more technologies out there that can help you with precision fertiliser application.

Put it in places that need it where nitrogen is low. These technologies are coming or are already out there.

If you're a livestock farmer consider reducing stocking rate.

If you're able to produce the same amount of product with fewer animals,

then that means the animals don't need as much maintenance feed and that means you don't need as much nitrogen inputs such as fertiliser or supplementary feed.

Which means less N in the system and that will have a positive effect on nitrate leaching as well. So it's a win win scenario.

In cropping systems the main source of nitrous oxide is the fertiliser that is applied to the crops.

So fertiliser timing rates and scheduling is key in terms of minimising nitrous oxide emissions.

And making sure that most of the nitrogen is used for plant growth.

CARRIE GREEN:
Right now there isn't one single solution for reducing nitrous oxide emissions.

The most reliable option is to cut back the amount of nitrogen hitting your soil – by lowering stock numbers, reducing supplementary feeds or using less fertiliser.

Reducing nitrogen in your soil will also reduce nitrate leaching.

Scientists are working hard to find solutions to reduce nitrous oxide.

You can keep up to date with all the developments on www.agmatters.nz

Actions to reduce nitrous oxide

How does nitrous oxide contribute to climate change?

As well as being highly effective at trapping heat, nitrous oxide is a long-lived greenhouse gas, like carbon dioxide. So, from a climate change perspective, the warming caused by every new nitrous oxide emission today adds to the warming caused by past emissions. Each emission lasts in the atmosphere for over a century, and the warming it causes continues for several more centuries after it has disappeared.

Globally, nitrous oxide has increased about 16% since pre-industrial times.

According to the latest New Zealand Greenhouse Gas Inventory, in 2019, nitrous oxide accounted for around 10% of New Zealand's total greenhouse gas emissions. That compares with carbon dioxide at around 46% and methane at around 42%. Nitrous oxide accounts for around 20% of New Zealand's total agricultural greenhouse gas emissions.

New Zealand's emissions of nitrous oxide have risen by about 50% since 1990—mostly as a result of the expansion of the dairy sector and increased use of nitrogen-based fertilisers. By far the largest source of nitrous oxide emissions is livestock urine deposited onto soils.

Under the Climate Change Response (Zero Carbon) Amendment Act, the Government has set a target to reduce long-lived greenhouse gas emissions (carbon dioxide and nitrous oxide) to net zero (that is, emissions are matched by removals) by 2050.

Where does nitrous oxide come from?

Nitrous oxide emissions come from a range of sources, including fossil fuel combustion. In agriculture, nitrous oxide is emitted into the atmosphere when micro-organisms act on nitrogen introduced to the soil via animal urine and dung, synthetic fertilisers and legumes. About 1% of nitrogen in the soil, from any source, is lost as nitrous oxide.

Many farmers use nitrogen-based fertilisers, legumes or animal manures to enrich their soil with nitrogen and help crops and pastures flourish. When grazing ruminant livestock eat nitrogen-rich pastures or crops, they use only a fraction of the nitrogen consumed to support the production of meat and milk. They excrete most of it in urine and dung, which creates very concentrated nitrogen patches in the soil. For comparison, a urine patch can contain the equivalent of up to 1000 kg N per hectare, while fertiliser application rates are typically 30-50 kg N per hectare (although there may be several applications per year).

Nitrogen in the soil undergoes a range of transformations by micro-organisms (see diagram below). Some of the nitrogen is given off as ammonia through a process called volatilisation. Over time, this is redeposited as nitrogen in rainfall and eventually gives rise to nitrous oxide emissions.

One group of micro-organisms, called nitrifiers, transform ammonium (NH4) into nitrate (NO3) and a small amount of nitrous oxide is produced during this process, which is known as ‘nitrification’. Another group of micro-organisms, called denitrifiers, in turn convert some of the nitrate into nitrous oxide (a process called ‘denitrification’) which is emitted directly into the atmosphere.

Finally, some of the nitrate produced during nitrification isn't taken up by plants or converted by denitrifiers into nitrous oxide and just sits in the soil as nitrate. This can leach or run off in irrigation or rainwater and result in nitrous oxide emissions from rivers and lakes.

Nitrous Oxide Diagram v2
Nitrous oxide emissions from agriculture. Image: De Klein CAM, Pinares-Patino C, Waghorn GC (2008). Greenhouse gas emissions. Book chapter. Environmental Impacts of Pasture-Based Farming, pg 1-32

What can farmers do to reduce nitrous oxide emissions?

Currently, there are no simple solutions to reduce nitrous oxide emissions that will work consistently on all farms.

Right now, reducing emissions essentially comes down to reducing the amount of nitrogen in the farming system, and minimising the proportion of the excess nitrogen in the soil that is transformed into nitrous oxide.

Actions that will help you to achieve this can be found at the top of this page.

Considerable research is under way in New Zealand and overseas to identify and verify new approaches to reducing on-farm emissions of nitrous oxide. While none of these options is fully proven yet, a number are showing promise. You can find information on these approaches on the Future actions page.

Will initiatives to reduce nitrate leaching also reduce nitrous oxide emissions?

Leaching arises when there’s excess nitrogen in the soil. Nitrous oxide arises from nitrogen transformations in the soil: the more nitrogen there is, the more nitrous oxide is produced. Therefore, efforts to reduce the amount of nitrogen in the soil will reduce both leaching and nitrous oxide emissions.

Scientists are looking closely at practices they know will help reduce nitrate leaching to see how they affect nitrous oxide emissions. For example, they’re investigating if farmers can use catch crops such as oats to reduce excess nitrate in the soil at the end of winter, and how they can best schedule irrigation and fertiliser applications to minimise the risk of nitrogen loss via nitrate leaching and nitrous oxide emissions.

Case studies

Other helpful resources

For more on the sources and science of nitrous oxide, see: