AT first glance they could be mistaken for the world’s loneliest mobile phone towers.

But rather than helping people to phone a friend, the steel masts and high-tech sensors now appearing across a network of grazing properties are being used to communicate the story of how carbon is being captured in Australian cattle paddocks.

Covering areas of 10 to 50 hectares, the “flux towers” as they are called measure wind speed, along with changes or ‘fluxes’ in gas concentrations in the air, 20 times per second.

The data is then applied using a method called ‘eddy covariance’ to delineate the movement of carbon between the air and the ground in real time.

Changes in paddock conditions – such as preparing ground for planting, phases of pasture growth, wet conditions, dry conditions, and burning events – cause carbon to be either drawn down from the atmosphere into the soil, or lost from the soil into the atmosphere.

The key processes at play are photosynthesis and respiration, QUT soil scientist Professor Dave Rowlings explained at a recent field day at the Quinn family’s property Essex at Middlemount.

“Photosynthesis is what drives carbon going into the soil through the plants, and with respiration, just like humans, microbes break down that carbon in the plants and they breathe out CO₂.

“With the flux towers we measure the total amount of photosynthesis and the total amount of respiration.

“So we look at that balance between carbon going in through photosynthesis and carbon coming back out through respiration, and depending on that balance, if we have a positive or a negative, tells us if we’re a sink or a source.”

The output he says is “really, really high resolution data”.

“The crux of it is we’ve got a laser that’s measuring CO₂ and water vapour 20 times a second, and we pair that with a three-dimensional wind speed monitor, also at 20 times a second.

“So it tells us if the carbon that’s traveling across your landscape is enriched in CO₂ – so you’ve got a loss – or it’s or it’s depleted in CO₂ – so it’s been drawn down.

“And we do this 20 times a second, 24 hours day, 365 days a year.”

Decades old technology now helping to tell the cattle/carbon story

Eddy covariance flux towers are not new, having been used since 1951 to measure how ecosystems interact with the atmosphere. There are many in use, with the FLUXNET global research network incorporating more than 1000 flux towers worldwide.

But the idea of using flux towers for the purpose of measuring carbon flows on cattle properties is far more recent. (See more stories below about how the technology is being used in the US).

The concept was first applied in Australia by family-owned agricultural technology business and pasture legume supplier Agrimix in 2021, when it commissioned a large-scale research project with flux towers across a network of Queensland cattle properties in partnership with the Queensland University of Technology (QUT).

Peter Quinn, Essex, Marlborough and Agrimix founder Nick Kempe at a recent field day at Essex.

Flux towers do not come cheap, with each unit costing about $150,000 to establish. $11 million has been committed to the flux tower project to date, shared by Agrimix itself, private cattle businesses involved in the research and Meat & Livestock Australia.

Reducing the cost of on-farm carbon measurement

Proponents believe flux towers can dramatically lower the cost of on-farm carbon measurement for farmers, including those looking to participate in carbon credit offset schemes by adding carbon to the soil through changed management practices, such as introducing  deep-rooted legumes to existing pasture mixes.

The field day at Essex was told that carbon is very hard to measure accurately because of the spatial variability of soil carbon that occurs across a given area of land.

Large numbers of soil core samples are needed to adequately capture the spatial variability Professor Rowlings said, which is a labour-intensive and costly process.

The flux tower technology, and the data it is collecting to underpin future modelling, has the potential to make that cost much more affordable for producers, the field day was told.

In terms of the accuracy of the technology, the research had shown “very, very good correlations” between what flux towers are measuring and what intensive soil sampling is also showing from the same area of land.

What are flux towers on cattle properties showing so far?

One question Professor Rowlings said he is often asked is “can you actually sequester carbon?”

The research in Central Queensland was showing that deep rooted legumes can put “a lot of carbon down into soil”, he said, and was demonstrating that carbon can be sequestered and at rates where “carbon neutral beef is a real thing”.

“The potential is there,” he said.

Progardes Desmanthus pasture legume at Essex in Central Queensland.

“Unfortunately you’re not going to get Desmanthus (a deep tap-rooted legume) across all your properties, but at least on those areas, the potential is there.”

The technology is helping producers to understand where soil carbon losses can come from, and because it is being provided in near real time, to understand what they might be able to do to mitigate those losses, Agrimix agronomist Zac Geldoff said.

Not every property will require a flux tower in future, the field day was told.

Modelling from the data being collected enables the creation of “digital twins” of any property, allowing different management systems or climate variations to be simulated to determine how those changes would affect future soil carbon stocks on that property.

One property involved in the trial increased soil carbon from 33.6 tonnes per hectare to 34.4 tonnes per hectare over an 18 month period following blade ploughing and then adding deep-rooted legumes to the existing buffel pasture.

QUT now oversees a growing network of flux towers as part of the Australian Long-Term Agricultural Research (ALTAR) initiative. The agricultural network complements the existing Terrestrial Ecosystem Research Network (TERN), which primarily monitors natural systems. By embedding flux towers across diverse production landscapes, the ALTAR network generates long-term, high-resolution data that is critical not only for advancing scientific understanding but also for supporting the Australian beef industry’s sustainability narrative with robust, empirical evidence, the QUT team explained.

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