Reducing nitrous oxide emissions

Practical ways to improve nitrogen management on farm.

Nitrogen plays an important role in pasture and crop production, but not all of it ends up where you want it. Better nutrient management can help improve efficiency, reduce losses and support productive farm systems, while also helping to lower nitrous oxide emissions.

Watch this video: where nitrous oxide comes from

In this short video, Dr Cecile de Klein from BSI, 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?

Nitrous oxide is a greenhouse gas produced naturally in soils when nitrogen from fertiliser, effluent and animal urine is processed by soil microbes.

Like carbon dioxide, nitrous oxide stays in the atmosphere for a long time. Each emission remains in the atmosphere for more than 100 years, contributing to warming long after it is released.

Nitrous oxide makes up around 20% of New Zealand's agricultural greenhouse gas emissions. Most of these emissions come from livestock urine deposited onto soils, with nitrogen fertiliser also contributing.

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.

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 is produced naturally in soils as part of the nitrogen cycle.

Nitrogen enters the soil from a range of sources, including animal urine and dung, nitrogen fertiliser, effluent and legumes. Soil microbes then break down and transform this nitrogen into different forms that can be used by plants.

On livestock farms, animal urine is typically the largest source of nitrogen entering the soil. When grazing animals consume nitrogen in pasture and crops, much of it is returned to the soil in urine and dung. These deposits create concentrated patches of nitrogen that are processed by soil microbes.

As nitrogen moves through the soil, a small proportion is released as nitrous oxide. Some nitrogen may also move beyond the root zone and leach into waterways through drainage and runoff.

The diagram below shows how nitrogen moves through the soil and the pathways that can lead to nitrous oxide being produced.

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?

There is no single solution that will reduce nitrous oxide emissions on every farm. However, many of the actions that improve nitrogen use efficiency can also help reduce nitrous oxide emissions.

In simple terms, reducing nitrous oxide comes down to reducing excess nitrogen in the farming system and making sure more of it is used for productive plant growth.

On-farm proof:

Dion Gordon reduced nitrous oxide emissions by lowering nitrogen fertiliser use, reducing stocking rates and improving overall farm efficiency. Small changes across the system helped reduce nitrogen losses while maintaining profitability.

Read Dion's story →

"The key is making sure most of the nitrogen is used for plant growth." Dr Cécile de Klein

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.

At Silverton Pastoral, the Abbiss family use precision agriculture technology and targeted fertiliser applications to match inputs to crop requirements, helping improve nutrient efficiency across the farm.

Read the case study →