by Graham Lloyd
Before the US government conducted its first nuclear weapons test on July 16, 1945, scientists were concerned the so-called Trinity test could ignite a chain reaction with nitrogen in the air that would end life on earth. As a precaution, scientists did an order of magnitude calculation to test the theory. In the end the calculation showed the probability was vanishingly small and the test went ahead.
This calculation has become a reference point for mathematician and soil scientist John Crawford, who is concerned with making sure that the world's six billion people will be able to get something to eat. Crawford, from the University of Sydney Institute for Sustainable Solutions, is concerned that when the same calculation for the Trinity test is done for the world's agricultural land, the forecast may tell us that the world's soil will run out in 60 years.
"It is not to say that soil will disappear in 60 years, but when you consider the amount of topsoil lost in the past 100 years, that figure of 60 years starts not to look so daft.
"We talk about alternative energy," Crawford says. "There is no alternative soil."
With the world's population growing in number and wealth, food security is a prime concern for global decision-makers.
Climate change has added a new dimension to research into soil carbon, which is central to soil health and productivity as a possible way to lock up global carbon emissions. A US Studies Centre conference in Sydney this month heard how Australia is at the forefront of the scientific understanding of soil carbon and how policy-makers here are ahead of the curve when it comes to thinking about ways to reward farmers for improving soil quality by building carbon content.
The federal government is establishing a carbon trading framework that will reward good agricultural practice. Its climate adviser, Ross Garnaut, will explore the issue in an update to his 2008 climate change paper for the federal government.
And if former governor-general Michael Jeffery has his way, a network of best practice farms will be established around the nation to build awareness in the notoriously conservative farming community on the benefits of improving soil carbon and health.
Crawford says soil health is at the root of most of the challenges that society faces in the next 30 years - food security, water supply, energy, climate change and health.
"Soil is the basis for human health, and agriculture is the basis for civilisation and there is great historical evidence that most of the great ancient civilisations fell as a result of decline in their soil," he says.
"What we need to find are incentives to start giving farmers the resources they need to manage the eco-system services that we've all taken for granted, and soil being the major part of that."
For Rattan Lal, director of the carbon management and sequestration centre at Ohio State University's Ohio Agricultural Research and Development Centre, food security is the key issue.
"We are almost seven billion people now," he says. "Out of seven billion, more than one billion people are hungry, out of that 300 million are in the Indian subcontinent and by 2050 there will be 9.2 billion people.
"We cannot achieve that food security without improving the quality of the land, whether climate change happens or not - that is a point of secondary importance - food production is number one. And while we are putting the carbon back it also mitigates climate change."
For Lal, building soil carbon will involve paying farmers to return crop residues to the land. He says it is not about turning away from chemical fertilisers. "I am a very strict vegetarian," Lal says. "If we were to go 100 per cent organic we can feed a billion people.
"Which five billion will we choose should not have food?" he asks. "It is my duty to make sure everybody gets food."
He says: "Rich people can afford to eat organic at double the price but feeding seven billion it is not possible."
For Lal, improving agriculture in the Third World is the key. In the Indian state of Punjab, where Lal was born, there is a train called the Cancer Express because it takes people to a neighbouring city where there is a cancer hospital.
"The soil is so depleted and they put pesticides and nitrate and phosphate which go straight into the water," Lal says.
"Babies from the mother's milk are having pesticides. The cancer rate is very high."
In Africa, food production has stagnated since the 1960s. The crop yields of cereal, sorghum and millet have remained at one tonne per hectare per year. In Ohio, where Lal is based, corn yield is 10 tonnes per hectare per year.
"The quality of the soil is poor," Lal says. "It does not respond even when you put fertiliser or genetically modified products on it because the carbon concentration is low. But farmers there are so poor we have to jump-start it."
The rationale for the US Studies Centre's conference in Sydney was to bring together the best scientists from around the world to try to better understand what happens to soil carbon.
Crawford says what emerged from discussions was that some aspects of carbon and soil were not as complicated as first thought.
There is now a much better understanding of the intimate relationship between carbon and the physical structure of soil and the working engine of soil. Scientists agree there is a threshold carbon level of between 1.1 and 1.5 per cent in the surface layer, and if the carbon content goes below that then soil functions begin to deteriorate.
Most soils of Africa and Asia, and in some areas of Australia, have a carbon concentration as low as 0.1 per cent.
The techniques needed to return carbon to the soil are well known, but it can be a long process and the question is how to pay farmers to give up crop residues that are a valuable commodity in many parts of the world.
"Most farmers struggle year by year and they don't have the luxury of saying 'I need to turn some of the profit back into soil' because it can take some years to improve your return on that investment and it is just too far down the line," Lal says.
Lal thinks a carbon price of between $20 to $25 a tonne for soil carbon is realistic.
"We're not talking about subsidies: we're talking about payments for eco-system services."
Verification is key. Alex McBratney from the University of Sydney has developed a carbon mapping tool as part of a research project, that has so far mapped a 120,000 square kilometre area stretching from the Queensland border to Griffith in NSW.
"Our research has been framed in the context of an emissions trading scheme, where the addition of soil carbon would be seen as an offset. To make that market operate well with confidence we need an independent auditor.
"If we could even have a very tiny increase in carbon across all range lands that would have a huge impact across all the country because we have so much range lands," McBratney says.