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Laser has bright future in nitrous oxide emissions measurement
A modest-looking metal box sitting in a Waikato paddock may seem unassuming at first glance, but what’s on the inside has the potential to transform the way greenhouse gas emissions are measured.
The box contains state-of-the art technology called a Quantum Cascade Laser, and it’s helping scientists funded by the New Zealand Agricultural Greenhouse Gas Research Centre get a much clearer picture of nitrous oxide emissions produced by farming.
Nitrous oxide (N2O) is an important component of New Zealand’s greenhouse gas emissions profile. It predominantly comes from agriculture, and from livestock urine patches in particular—the nitrogen content in urine is more than plants can use, so the excess is transformed through microbial processes into nitrous oxide.
Professor Louis Schipper from the University of Waikato is co-leading this part of the NZAGRC’s research programme into nitrous oxide emission mitigation. He says because urine patches are so scattered, it can be difficult to measure nitrous oxide at the paddock scale.
“In the past we’ve measured nitrous oxide emissions using chambers, which are small enclosures that fit over the soil—they take samples over time to give us a production rate of the gas,” says Professor Schipper.
“But you need a lot of chambers—and a lot of time—to try and measure emissions from all urine patches. It’s an enormous task and the variability is very hard to capture.”
He says while methodologies have been developed to deal with that variability—and chambers continue to have a very useful role in the science of measuring agricultural greenhouse gas emissions—there are still a lot of gaps in the data they provide.
This is why Professor Schipper and his team are now using a Quantum Cascade Laser (QCL), which was purchased recently by the University of Waikato. The QCL has been installed at the Troughton Farm research site in Waikato, which has been used to support a range of research projects to understand soil carbon and nitrous oxide emissions from New Zealand dairy farms.
“The current micro-meteorological technique we use—eddy covariance—allows us to measure the nitrous oxide emissions that are coming from the paddock as a whole, rather from individual urine patches,” says Professor Schipper. “While the technique has been around for a while, it’s been difficult to take measurements with sufficient precision. This is where the QCL is a game changer because it can determine nitrous oxide concentration very quickly, to an extremely high precision. It’s measuring ten times a second, to about 0.2 parts per billion—that’s unprecedented, and when practically applied to the paddock setting it’s a real breakthrough in terms of routine measurement.”
He says the QCL is able to continuously measure emissions of nitrous oxide over six to eight hectares, and integrate its measurements.
“There’s a pipe that draws air into the QCL—ours is mounted on a small tower and is about two metres off the ground,” explains Professor Schipper. “For every metre above the ground that the air is taken from, the QCL integrates measurements from over a 100 metre radius. That means if you place the air pipe two metres up you’re essentially measuring nitrous oxide over a 200 metre radius; if it’s three metres up you’re measuring a 300 metre radius, and so forth. You can choose how much area you want to measure.
“The device allows us to get an average measurement of how much a nitrous oxide a paddock is emitting, rather than what’s happening above just one patch,” he says. “It’s a bit like looking at an impressionist painting—if you zoom in on a single brush stroke you don’t get much of an idea what’s going on, but using the QCL we’re able to step back and see the bigger picture.”
Professor Schipper says the more detailed data from the QCL should also make it easier to develop models that will allow scientists to make predictions about nitrous oxide emissions in other locations.
“This technology is great but there’s still an important role for chambers, which are really useful for making comparisons between multiple treatments within a paddock,” says Professor Schipper. “In the end we want eddy covariance and chambers to be working together—that will give us the best results.”
He says he is very excited to be working with this kind of technology and seeing its potential.
“Yes it’s pretty fancy science, but we’re not losing sight of the long term goal of reducing greenhouse gas emissions—hopefully the QCL will make that easier.”
|Read more about Anne Wecking, who is working with the QCL as part of her PhD|