THE Coalition's plan to store carbon dioxide in soil as a central plank of its climate policy has been thrown into further doubt by new research showing Australian soils are unlikely to offer low-cost emissions cuts.
A University of Melbourne survey of hundreds of Australian studies going back three decades found that using the country's soils to offset a significant proportion of national greenhouse gases “is technically limited and economically unviable at the present time”.
Published in the journal Nature Scientific Reports, it suggests farmers would lose out through soil-carbon projects at carbon prices backed by both the government and the opposition.
Report co-author Rick Roush, the Dean of the Melbourne School of Land and Environment, said most active soil scientists thought it would be "a stretch” for farmers to use the Carbon Farming Initiative – a policy that encourages soil-carbon projects and is backed by both major parties.
At the current carbon price – $24.15 per tonne – farmers would stand to lose at least $12 per tonne for carbon farming under normal soil conditions, the researchers found.
The shortfall under the government's plan would be even greater if its decision to move to a floating carbon price from next July is implemented. At Tuesday's announcement of the plan to shift from a fixed to a floating carbon price a year earlier than scheduled, the government estimated the price would drop to as low as $6 a tonne.
The impact of the study, though, may fall harder on the viability of the Coalition's rival Direct Action plan.
In 2010, the opposition described carbon farming as “the single largest opportunity for carbon dioxide emissions reduction in Australia”, accounting for about 60 per cent of emission cuts.
"The Coalition will use the Emissions Reduction Fund to deliver about 85 million tonnes per annum of CO2 abatement through soil carbons by 2020," the Coalition said in a media release. The plans include paying farmers $10 per tonne for carbon farming.
“Our analysis showed that these strategies would result in only 53.3 million tonnes of CO2 equivalent sequestered in soil and would therefore not meet the 85 million tonnes targeted in the Coalition's Direct Action Plan,” Professor Roush said.
The opposition's climate spokesman, Greg Hunt, said the carbon farming figures were always indicative figures for both price and quantity, with the market to set both. The budget had not changed and emissions reductions would be achieved within it, he said.
"Having met with Greening Australia and major carbon-farming participants throughout the country in the last few weeks, the potential for reducing land-sector emissions is greater than we ever expected,” Mr Hunt said.
Sequestering carbon would likely be restricted to the top 10 centimetres of soil, and be limited by low-nutrient levels and water scarcity. Application of fertiliser would boost the sink capacity of soils but at a rising cost to farmers, Professor Roush said.
Carbon is slow to accumulate in the soil, and the agricultural methods mostly likely to encourage it, such as no-till farming, are already widely used, he said.
While the survey focused on Australian studies, Professor Roush said carbon bio-sequestration may not have much greater promise overseas.
“Our gut suspicion is that it will also be disappointing even in areas that have better rainfall and better soil fertility to start with, for the same reasons,’’ he said. ‘‘It’s difficult to keep soil carbons accumulating when you continue to plough and cultivate annual crops.”
However, additional research by another of the report’s authors, the University of Melbourne's Professor Deli Chen, into keeping nitrogen fertiliser in the soil may be much more promising not least because some of it converts into nitrous oxide with 300 times the greenhouse potency of carbon dioxide.
“It would be a far better investment to focus on managing nitrogen fertiliser use than soil carbon, per se.”