Carbon farmers are raring to go, but experts say the soil carbon method is flawed

Carbon farming proponents are preparing for a bumper year in earning carbon credits from a $4.5 billion government initiative, but several experts say current methods for measuring how much carbon can be trapped in the soil are flawed.

Soil carbon farming, or sequestration, sucks carbon dioxide from the atmosphere and locks it in the ground, offsetting greenhouse gas emissions and, at the same time, improving soil fertility.

West Gippsland farmer Niels Olsen invented a planter that regenerates the soil and improves carbon retention. Credit: Joe Armao

The government has allocated $4.5 billion to purchase carbon credits under its Emissions Reduction Fund, which launched in 2015, and it has committed to funding ongoing payments for projects that offset greenhouse gases.

But so far, only a single farmer, Niels Olsen in West Gippsland, has earned any carbon credits for his soil.

The industry hopes that will change this year because of the Albanese government’s moves to legislate stronger climate action and offer financial incentives to offset carbon emissions.

Last week the government revealed the details of its signature climate policy, the safeguard mechanism, which forces the country’s biggest polluters to cut their emissions by 30 per cent by 2030 under binding pollution caps. Under that scheme, credits earned sequestering carbon can be sold to companies that cannot reduce their own emissions in line with the cap.

AgriProve, the largest soil carbon project developer, says it is in the final stages of auditing 15 carbon farming projects.

“We want to move from talking about the potential to demonstrating the potential,” said managing director Matthew Warnken.

Olsen, who invented a seed planter to mulch and aerate the soil as it plants seeds, said his latest soil tests show each hectare of his 100-hectare farm is pulling 26 tonnes of CO2-equivalent out of the atmosphere each year. At today’s carbon credit spot price of about $33 per tonne, that’s more than $850 a hectare.

“The ramp-up in the last 12 months has been just phenomenal,” he said. “And there are more and more farmers coming on board being able to do what we’ve done.”

Carbon is the foundation of life. It is also the foundation of Earth’s climate crisis. Soil sequestration harnesses the first attribute to fight the second.

Healthy, fertile soils contain lots of carbon in the form of alive and decomposing plants – plus the worms and bacteria that feed on them – but generations of intensive agricultural practices have stripped carbon from the world’s farmland. Putting as much carbon back as possible is crucial to making agriculture sustainable.

Plants use sunlight and CO2 to photosynthesize, turning atmospheric carbon into new roots and leaves. As those roots decay, they lock carbon in the soil, where it feeds a teeming underground world of microbes and worms. Farmers can give them that chance by keeping more plant cover, running fewer animals and minimising erosion.

Among scientists, there is no doubt increasing carbon in the soil is a good idea, but several told The Age and The Sydney Morning Herald they were sceptical that changes to soil carbon could be accurately measured in a cost-effective way with current technology. Without those measurements, it is impossible to know if farmers are really doing what they claim, they said.

“The soil carbon method is flawed,” said Professor Andrew Macintosh, inaugural chairman of the federal government’s Emissions Reduction Fund assurance committee.

Leaves, debris and soil from different plots packed into brown paper bags. In the lab, the material is dehydrated to calculate how much carbon it contains.Credit: Alana Paterson for The Washington Post.

“There is considerable scope for gaming with the conduct of measurement, primarily because it is not possible to police and verify compliance with the measurement protocols.”

The core problem is the soil’s inherent variability. “You don’t really know what’s under the surface. Soils vary from centimetre to centimetre,” said Associate Professor Matthew Harrison, who studies soil carbon at the Tasmanian Institute of Agriculture. “It’s incredibly challenging.”

To get a carbon measure, a farmer will employ a contractor to dig sample holes across the property. The dirt from these holes is dried, crushed, sieved and the roots removed. It is then ground up and sent to a laboratory.

This is costly and time-consuming, so farmers want to make as few holes as possible. Hence, the industry generally averages about one test per 10 to 15 hectares. That is nowhere near the level needed for accurately measuring soil carbon, said University of Melbourne soil carbon expert Robert White. He put it closer to one test for every hectare.

Professor Peter Grace, who is studying soil carbon measurement at the Queensland University of Technology, compared the current testing method to “throwing a spoonful of water into a bathtub”.

A spokesman for the Clean Energy Regulator said soil measures for carbon credits “were based on the best available, recent science” using work done by CSIRO and the University of Sydney in 2021.

Professor Alex McBratney, a world-leading soil scientist at the University of Sydney and a member of the government’s Emissions Reduction Assurance Committee, said soil tests were challenging but not impossible.

“The soil carbon method we have in Australia is the best in the world,” he said. “These difficulties will be overcome.”

A review released last week of Australia’s carbon credit system did not make specific findings on soil carbon, but concluded the system was basically sound.

On a farm near Cressy, Tasmania, Professor Mark Adams, a soil researcher at Swinburne University, has installed three six-metre towers that measure the concentration of CO2 in the air above the farm and how much is being taken up by the soil.

If the technology can be made to work – it’s being tested in other places as well – it could be a cheap, accurate replacement for soil cores.

But while the industry is ready for take-off, the science is not, Adams said.

“Our methods for measuring it are not fantastic, even after all these years,” he said. “The sustainability of soil carbon credits is very much in question.”

Roderic O’Conner lent Adams his land for the testing. He has been hearing about golden carbon harvests for years.

“I know bullshit when I hear it,” he said.

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