Wednesday, April 24, 2024

PULPIT: Finding ways to reduce nitrous oxide

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In the second of two articles about nitrous oxide, AgResearch principal scientist Dr Cecile de Klein outlines research into technologies and practices aimed at reducing nitrous oxide emissions from New Zealand farms.
Reading Time: 3 minutes

In my first article, I described how naturally occurring microbes convert nitrogen in the soil into nitrous oxide, which is emitted into the atmosphere. I explained that nitrous oxide is a potent and long-lived greenhouse gas that needs to be addressed if NZ is to achieve its emissions reduction targets.

I also explained that some common agricultural practices, as well as the urine and dung of grazing livestock, add significant amounts of nitrogen to the soil. This can lead to increased emissions of nitrous oxide.

In this article, I’ll look at some of the work my colleagues and I have been doing to identify and test technologies and practices aimed at reducing emissions of nitrous oxide from NZ farms.

Research in NZ, funded by the NZ Agricultural Greenhouse Gas Research Centre (NZAGRC), has two broad goals:

•Identifying ways that farmers and growers can reduce the amount of nitrogen entering the soil

•Finding ways of reducing the microbial activity in the soil that converts nitrogen into nitrous oxide.

That research – along with the actions of forward-thinking NZ farmers – has already proven conclusively that some currently available practices can reduce the amount of nitrogen entering the farm system.

Many livestock farmers have worked hard to improve the productivity of individual animals so that stock numbers can be reduced without compromising overall farm productivity. Fewer animals with the same total farm production means less feed eaten and less urine and dung excreted, so less nitrogen ends up in the soil where it can be converted to nitrous oxide. 

On the cropping side, some growers are using precision technology to calculate and deliver exact doses of nitrogen-based fertiliser and irrigation water only to those parts of the farm that need it. Targeting and optimising inputs of nitrogen in this way ensures crop yields are maintained while minimising the amount of nitrogen available in the soil for conversion to nitrous oxide. 

There are some great videos on the Ag Matters website showcasing the positive results achieved by NZ farmers who have taken these and similar steps to reduce their inputs. Their actions might not transfer to all farms, but their stories might inspire other farmers on their journey towards improved sustainability.

But what about technologies and practices for reducing nitrous oxide emissions that might be available in the future?

Nitrification inhibitors

The search for new nitrification inhibitors suitable for NZ environments and regulatory standards is well-advanced.

Nitrification inhibitors are chemical compounds that suppress the action of nitrifying microbes in the soil which convert nitrogen into nitrate and emit nitrous oxide as a byproduct.

Nitrification inhibitors can be added to fertilisers or spread directly onto grazed pasture. They are widely available overseas and, until 2011, an inhibitor called dicyandiamide (DCD) was used on some NZ farms. However, the discovery of residues in milk led to the withdrawal of DCD from the NZ market.

Recent research in the laboratory has identified promising alternative compounds, and testing is now under way in the field. The research will rigorously assess the long-term impacts of these compounds on the environment, animal health and welfare and product quality.

Alternative feed crops

Comprehensive research is also exploring the potential of alternative feed crops to reduce nitrous oxide emissions.

We’ve already proven conclusively that when animals consume sufficient quantities of alternative feeds such as plantain, fodder beet and maize silage, they excrete lower concentrations of nitrogen in their urine and dung. This is simply because these feeds contain less nitrogen than the pasture and feed species typically used on NZ farms.

However, more work is needed to understand the proportion required in the animals’ diet for the nitrogen reduction to be meaningful. We also need to assess whether results are consistent across different farm systems, soil types, climate zones and seasons, and how best to incorporate the different feeds into our predominantly grass-based systems, including understanding any unintended consequences for soil carbon stocks.

Researchers are particularly interested in plantain, as well as demonstrably reducing the amount of nitrogen excreted by animals that consume it. There’s evidence that growing plantain reduces the activity of some of the soil microbes responsible for nitrous oxide emissions. 

We need to learn a lot more about the mechanisms and variables behind this effect, but if it’s confirmed that plantain has this double impact that’s great news for livestock farmers.

Any solutions put forward by the research community need to be practical, cost-effective and proven to work across the range of NZ farm systems and physical environments.

And those solutions must be rigorously tested to ensure reduced emissions of nitrous oxide aren’t offset by increased emissions of other greenhouse gases – or by some other adverse environmental impact.

You can keep up to date on all of our research into reducing nitrous oxide emissions on the Ag Matters website.

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