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The Morrison government is backing soil carbon – drawing carbon from the atmosphere and storing it in the land – as a major part of its response to the climate crisis.
The idea isn’t new, and at times has been derided as “soil magic” due to exorbitant claims about what it could achieve. But it is receiving renewed focus after the government listed it as one of five priority areas under its so-called “technology, not taxes” approach to reducing greenhouse gas emissions.
The agriculture minister, David Littleproud, has flagged that farmers should expect more support for soil carbon and other carbon farming projects in the May budget. Meanwhile, other Nationals MPs have rejected any steps to tackle the climate crisis and called for agriculture to be exempt from a target of reaching net zero emissions, should the government ever commit to one.
So what is the truth about soil carbon? What role can it – and agriculture generally – play in reducing emissions?
Do we know how much extra carbon could be stored in soils?
The government’s roadmap says if management was improved on a quarter of crop and grazing lands in Australia this could draw “between 35 and 90 million tonnes of CO₂ per annum from the atmosphere while improving agricultural productivity and soil resilience”.
But that estimate could be out of date.
For those numbers, the roadmap points to work completed at CSIRO in 2010 by Dr Jonathan Sanderman, who is now a soil scientist at the influential Woodwell Climate Research Center in Massachusetts.
“It’s possible that sequestration rates are much higher than those average values in that report,” Sanderman says.
He said the calculations were based on best-practice soil management back then, and there are more options available now to farmers.
But he says even though he spends his life advocating for better soil management there is “too much attention” on soil carbon.
“It’s a positive story and farmers can do something positive for the world and improve their own sustainability and draw some carbon out of the atmosphere. But it is easier to achieve real reductions [in emissions] in the energy sector and people are forgetting that.
“I see soils and other solutions like restoring coastal wetlands as important, but they’re in addition to getting off fossil fuels.
“If we have any chance of maintaining a safe climate, we have to get off fossil fuels as quickly as possible and then pull a large amount of CO2 out of the atmosphere, and soil carbon can contribute to that drawdown.”
For context, the government’s lower end estimate for soil carbon storage of 35mt CO2 per year is less than the 48.4mt emitted by Australia’s four highest climate polluting coal plants.
How do you get carbon back into soil?
When soil gets disturbed, for example through tillage, it exposes the organic matter to the air, oxidising the carbon within it and producing CO2.
“In our agricultural soils, we’ve lost about half the carbon that was there in the first place,” says Prof Alex McBratney, director of the Sydney Institute of Agriculture at the University of Sydney.
“You need to increase the plant biomass on an annual basis – that will increase the carbon. Most methods are either based directly on plants or the microbes growing in it.
“The basic idea is that you produce below-ground biomass – that’s plant material, more roots.”
What does the government want to do, and will the carbon stay put?
The Clean Energy Regulator says the government’s Emissions Reduction Fund has so far awarded 14 contracts to store carbon in soils, with the first of those being awarded in 2015.
In total, those carbon abatement contracts are worth about 14mt of CO2e.
The Morrison government’s technology roadmap focuses on cutting the cost of measuring soil carbon which “is a barrier to widespread adoption of practices that would unlock soil carbon sequestration on a broad scale”.
All experts the Guardian spoke with agreed that cutting the cost of measuring soil carbon was a good step.
There was no question either that increasing the organic matter in soils has a host of added benefits, including higher fertility levels, better water retention and prolonged resistance to drought.
“It’s good for the soil and that means it’s good for crops and pasture and the productivity and profitability of the farms,” says Dr Michael Crawford, chief executive of the government-backed Soils CRC research hub.
But he says farmers need a lot more than just a cheaper soil carbon measuring method.
“Australian soils and our climate and our farming systems don’t lend themselves to storing great amounts of carbon,” he says.
Australian crop growers have been practising methods advocated for improving soil carbon for decades, he says, “and soil carbon levels haven’t changed all that much”.
There is still much more research needed, he says, to give farmers different options to improve their soils in all the different climates across the country.
There are also issues of permanence – how long is the carbon is stored for?
Crawford, Sanderman and McBratney all point out that if those improved farm practices stopped then carbon can make its way out of the soils over a matter of a few years. Drought can also see soils lose carbon.
What about all that methane?
Australia’s agricultural sector is currently responsible for about 13% of national emissions.
A large chunk of that comes from the methane that’s belched (and it is mostly belched) out of livestock.
In 2017, Meat and Livestock Australia (MLA) – the red meat industry’s research and marketing body – launched a program to push the sector to be carbon neutral by 2030.
A roadmap for the project, released in December 2020, said in 2017 the industry’s footprint was 55.7mt of CO2e, with about 40mt attributed to the methane that originates in the cow’s stomach.
As well as giving off methane – a greenhouse gas that is 50 times more potent at warming the planet than carbon dioxide (measured over a 20-year period) – the animal’s production of that gas is also lost energy.
Doug McNicholl, sustainability investment manager at MLA, says there are simple ways farmers can reduce methane levels “but the basic action first is that you can’t manage what you can’t measure, so we want farmers to understand what livestock they have and the classes of them and then they utilise the tools available.”
Can seaweed cut a cow’s carbon?
McNicholl says farmers can do a lot already to cut methane emissions. Selecting animals that produce less methane is now becoming possible, he said. Different mixes of foraging plants can also cut methane.
There are also feed additives being developed – one synthetic and one based on seaweed – that could drastically cut the methane production.
Dr Michael Battaglia is research director for sustainability at CSIRO and a director of a FutureFeed – a company developing a feed supplement derived from a red seaweed species called Asparagopsis.
There are claims the seaweed could cut methane by as much as 98% – but that figure should come with many caveats.
In Australian experiments in a feedlot, where beef cattle spend their last three months or so, the additive almost eliminated the methane production.
Earlier this month the government awarded a $1m grant to a Tasmania-based company, Sea Forest, to develop and increase production of the seaweed.
Battaglia says about half the emissions of methane in beef cattle comes in their final days in a feedlot, where a seaweed supplement would be easy to roll out.
The job of feeding animals daily with the supplement gets harder for cows out on pasture or in the outback.
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