THE rich, dark soils of Australia's farming heartland contain more carbon than every coal-fired power station in the country could pump out in a century.
Tweaking the balance so the earth can soak up just a little more CO2, by changing the way crops are grown and by turning some cropland into pasture, could theoretically fulfil all of Australia's greenhouse gas targets in one hit.
Both the Government and the Opposition believe rural landscapes can play a big role in meeting emissions targets, provided the climate agreement being debated in Copenhagen changes existing rules so that biosequestration can be used as an offset for industrial carbon output.
Unfortunately things are much more complicated than simply digging more organic fertiliser into the soil, and experts doubt whether ''green carbon'' solutions can ever be more than a sideshow to more direct ways of cutting carbon emissions.
''It could have a role in significantly reducing emissions in the short term, though its long term value is going to be limited,'' said a leading CSIRO soil carbon expert, Dr Jeffrey Baldock. ''It's not going to be a way of allowing the world to keep burning fossil fuels.''
Soil carbon sequestration means getting more carbon-based life into the earth, in the form of plant fragments and the tiny organisms that break them down.
The problem is that microbes break down plant matter and return it to the air at the same rate as it is buried in the soil.
The CSIRO uses the analogy of a leaking bucket to explain the cycle, saying no matter how much water you put in, the same amount will leak out again.
The hope of biosequestration lies in changing land management practices, so that soils have more plant matter and nutrients. This can be achieved by changing crop rotations, letting stubble decay into the ground after harvests, and topping up soil with organic material.
The leaky bucket would be replaced with a bigger bucket; it would still leak at the same rate but it would hold more water at any one time.
Some farmers are seeing dollar signs in the idea, because carbon credits could be created by changing the way a property was managed to soak up more carbon from the air. But with potential benefits come liabilities as well.
The current international framework for measuring land use change and forestry means that losses in carbon sequestration through uncontrollable events such as bushfires are counted against any benefits.
The National Farmers Federation sent a delegation to the Copenhagen talks to argue that farmers should have the right to opt in to emissions trading schemes but should not be punished if drought or fire ruins their sequestration plans.
Another problem is the lack of a high carbon price needed as an incentive to change land management practices.
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