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Soil carbon questions

On soil carbon, two schools of thought share the same track, often uncomfortably. One school, which includes the United Nations, sees the potential of soil carbon to pull huge amounts of carbon dioxide from the atmosphere, at least temporarily, giving humanity time to think about more lasting solutions to climate change. The other sees overwhelming complexity in trying to get this to happen, especially in ways that can be measured and incorporated into a carbon trading program. Often these thoughts inhabit the same people, as is the case with Dr Jeff Baldock, who leads CSIRO’s Soil Carbon and Nitrogen Balance in Agricultural Lands program. Dr Baldock thinks carbon should be sequestered in soils for its own sake. Most of Australia’s agricultural land has less than half the carbon it did before European settlement, and that adversely affects water-holding capacity, soil biology and resilience. He also thinks the Carbon Farming Initiative may deliver a soil carbon methodology in 2013. “Whether the economics around it, and all the other elements relating to carbon accounting, persuade people to take advantage of it is another question.” Dr Baldock’s current brief is to look at whether there are practices that can reliably sequester soil carbon, and whether that sequestration can be retained and reported in ways that satisfy a commercial market. On the latter issue, there is progress. Dr Baldock said that spectroscopy, which beams energy at the soil and interprets the signals that bounce back, promises most of the accuracy of lab-based soil sampling methods, but at 10-20 per cent of the cost. At the moment, spectroscopy can only be used on a site-by-site basis, but developmental work within CSIRO is establishing whether units can be attached to tractors or quad bikes to take a continuous reading of soil properties, as a yield monitor continuously reads a crop. If the spectroscopy work lives up to its promise, Dr Baldock said it could be an integral part of a Carbon Farming Initiative methodology for soil carbon. But putting together a workable methodology is much harder than sorting out the mechanics of soil sampling. Carbon has to be accounted for across different management practices, on different soils, in different climates and across time. And because of permanency requirements, a methodology currently has to provide a way of accounting for soil carbon over 100 years. The farmers he talks to won’t engage with the CFI because of the 100-year rule, Dr Baldock said. But the rule, or something like it, won’t just go away. “The definition of sequestration is permament removal of carbon dioxide from the atmosphere. Permament removal – not 25 years, not 100 years,” he said. “But no-one will go into a scheme that’s longer than 100 years, and they’re not even going for that.” While this policy issue is thrashed through, Dr Baldock is pondering other aspects of the soil carbon puzzle. “When you think about it, farmers are currently paid to remove carbon from their soil in the form of grain or beef. “Right now it’s more economically viable to produce as much grain as possible, rather than to put as much carbon into the ground as possible. “But one of the things we haven’t done well yet is to work out the benefit of building carbon for a carbon accounting scheme, and also for the extra productivity. “People say it’s going to be difficult to make carbon accounting pay for itself because of costs and the low value of carbon. “But if building carbon boosts your productivity by 10 per cent, then the economic analysis should include that as well.” So far, he said, little work has been done that allows scientists to predict how improving soil carbon levels will affect productivity.

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