Thursday, March 28, 2024

Laser throws light on emissions

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As farmers and researchers grapple with nitrate losses into waterways and nitrous oxide to the air, half the challenge has been how best to measure them to even begin to better understand their behaviour. Richard Rennie spoke to scientist Louis Schipper.
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A quantum cascade laser sounds like something from Dr Who and like his police box popping up in odd places, one has appeared in a Waikato paddock.

It’s got Waikato University biogeochemistry Professor Louis Schipper excited.

He is co-lead in the New Zealand Agricultural Greenhouse Gas Research Centre’s research programme into nitrous oxide.

His latest piece of kit is the quantum cascade laser, a quarter of a million dollars investment that is painting a “big picture” view of the level of nitrous oxide losses on a dairy farm.

It was bought by the university and the research is funded by the centre.

The laser works on the principal that every molecule absorbs light at a very precise frequency. It emits light in the mid to far infrared radiation end of the electromagnetic spectrum.

The high energy output and ability to be fine-tuned to specific frequencies make the laser ideal for quantifying specific gases and pollutants in the atmosphere.

Having been commercialised only within the last decade or so, its uses are still unfolding and include breath testing humans.

The machine can detect nitrous oxide molecules emitted from cow urine patches across a whole paddock, measuring 10 times a second down to 0.2 parts per billion – speed and precision Schipper says have been unprecedented till now.

The measurements can be done over an area of six to eight hectares, making the laser ideal for farm scale research, thus allowing scientists to look at management practices.

The reason for the focus on nitrous oxide is its inherent strength as a greenhouse gas.

“We are talking a gas that is 300 times more potent than carbon dioxide per molecule in terms of greenhouse gas warming ability, so a little does go a long way.”

It is a gas that bedevils livestock systems, along with methane, and one that till now has been measured only using chambers about the size of the average rubbish bin lid.

“They are small enclosures that fit over the soil and gas samples are taken with time to determine nitrous oxide emissions.

“Unfortunately, though, these chambers can cover only a small area and, of course, with cows urinating on 5% of a paddock area, it can be a big job to capture all the spatial variability.”

However, he is also quick to defend the chamber method because it is invaluable for comparing different methods of reducing nitrous oxide emissions.

Schipper says the laser has come to be the hub for a team of experienced researchers from multiple disciplines including Associate Professor Dave Campbell and Dr Liyin Liang, covering farm systems, soil science and greenhouse gas research. Recently, they have been joined by Anne Wecking who will do her doctorate using the laser.

The researchers include experts in eddy covariance, a micro-meteorological technique that can record and analyse the fluctuations in air currents and movement in the emission area.

Coupled with the nitrous oxide concentrations measured by the laser, researchers now have a very clear helicopter view of the losses in a paddock, something Schipper likens to looking at an impressionist painting.

“If you zoom in on a single brush stroke you don’t get much of an idea of what is going on but the laser allows us to step back and get a far bigger picture.”

With the machine running since last November, Schipper and his colleagues have been harvesting data that has left them both excited and challenged by what they are finding.

“What we have found really interesting is when cows go into a paddock and deposit lots of urine and dung patches there is only a small blip in nitrous oxide emissions.

“It is only the first rain after that when nitrous oxide emissions go berserk on the dry soil.

“Just a few millimetres of rain on the very top 1-2cm of the soil surface is enough to accelerate nitrous oxide emissions.”

Researchers have also discovered a pattern of nitrous oxide losses with peaks and troughs in gas emissions depending on the time of day.

“This is an area we have just recognised and really want to do some more work on.

“So, we have already learned that the losses are dependent on time, temperature and moisture.

“We have got rid of a lot of the noise you can get in research and can measure the full mix of different aged urine patches. They all light up differently under the laser.”

Schipper is excited by the prospect of using the machine to test mitigation techniques on a farm-scale level, being able to observe and include allowances for farm system changes like stocking rates.

One of the first trials will be to observe how well plantain in a pasture sward might reduce nitrous oxide emissions.

The work leaves Schipper feeling very optimistic about the industry’s ability to mitigate nitrous oxide losses.

“In my classes I always try to end as much as I can on a positive success story.

“One of them is how the world reduced the ozone hole by reducing chlorofluorocarbon use. It required commitment but it is being done – the problems are there but so are the solutions.”

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