Magazine article Geographical

Dishing the Dirt: Much of the Time We Treat It like Dirt, but Could the Humble Farm Field Hold the Key to Fighting Climate Change?

Magazine article Geographical

Dishing the Dirt: Much of the Time We Treat It like Dirt, but Could the Humble Farm Field Hold the Key to Fighting Climate Change?

Article excerpt

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THERE'S A NEW CROP THAT HAS increasing numbers of Australian farmers excited, but it has nothing to do with wool, wheat or beef. You can't see it, you can't eat it and you can't win prizes with it at the local agricultural show. But farmers are hoping it will not only heal their struggling soils but make them players in the new global carbon economy. For much of the past decade, large areas of Australia have been in the grip of drought. Some argue that it's just another dry spell in a country with a reputation for droughts and flooding rains, but the majority now agree that drier times are here to stay. For example, rainfall has plummeted in the Murray-Darling river basin, a vast area where more than a fifth of Australia's food is grown. Indeed, by 2030, the predictions are that the Murray-Darling area will receive 41 per cent less rainfall as a result of climate change. While these forecasts have some farmers throwing their hands up in defeat, others believe they could continue doing business into a drier future, using a strategy called 'carbon farming'. This simply means using the plants you grow on your farm to 'harvest' carbon from the atmosphere and return it to the soil.

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Dr Brian Murphy, a senior soil scientist with the New South Wales Department of Environment and Climate Change, explains: 'First, the leaves of the plant absorb carbon dioxide, which finds its way to the growing root system. The roots exude chemicals (containing carbon molecules) into the soil, which attract fungi. The fungi grow on the roots and assimilate the carbon, and eventually, as the roots slough off and break down, the carbon becomes incorporated into the soil.'

The potential for sequestering carbon in soils, some researchers say, is huge, and Alex McBratney, professor of soil science at the University of Sydney, has calculated just how much. If the carbon content of a quarter of the world's soils was increased by just one per cent (by changing agricultural practices), he says, it would result in the removal of 300 gigatonnes of C[O.sub.2] from the atmosphere. This is roughly 330 times more than all of the greenhouse gases emitted by the UK in 2003. While not all soils have the capacity to sequester much more carbon (for example, sandy soils and those in very dry areas), supporters of soil carbon sequestration say we've barely scratched the surface.

But while farmers are happy that they can help remove carbon from the atmosphere, they are even more interested in the fact that a high carbon content can buffer a soil against climate change. 'Soils can respond to extreme events better if the carbon content is high,' says Dr Jeffrey Baldock, a research leader with the land and water division of Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). If the soil contains plenty of carbon, he says, it will be able to retain more water, cope better with temperature extremes and retain more nutrients.

Australian soils now contain only about half the carbon they did before European settlement. Ploughing, burning stubble and removing crop waste gradually strips the carbon from the soil, leaving it without structure and unable to hold much water.

Murphy says improving agricultural practices can increase the amount of carbon being 'fixed' in the soil. The soil under an intensively farmed wheat crop (cultivated six times a year and the stubble burnt after the harvest) will contain about 20-23 tonnes of carbon per hectare, but soil under the same crop grown using no cultivation and no burning may have as much as 30 tonnes of carbon per hectare. That's close to a 50 per cent increase in carbon capture.

THE IDEALIST

David Marsh started out as a regular farmer, but had an epiphany about ten years ago when he realised the effect that his activities were having on the environment. Today, he's an advocate of the 'planned grazing' method on his 800-hectare property in the Boorowa district, four hours' drive southwest of Sydney. …

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