Science goes back to the soil carbon riddle
(Project: Hamilton Stubble Nutrient)
November 2008
A TRIAL into storing carbon in cropping land may have an impact on the role of grain production in future emission trading schemes (ETS).
CSIRO researcher, Clive Kirkby believes he has found an answer to the riddle why soil carbon levels did not necessarily increase – even when best practice conservation farming techniques were employed.
Dr Kirkby’s preliminary hypothesis is that nitrogen, phosphorus and sulphur are required to increase soil carbon levels.
If these nutrients are not available to microbes, then carbon levels will not increase, with carbon from decaying crop residue volatilising.
Dr Kirkby told a Southern Farming Systems (SFS) field day at Dunkeld while there were no hard results from trial work conducted through SFS, early signs suggested that there was strong correlation between N, P and S levels and carbon.
If the theory could be proven, it will have an important role in dealing grain production into the carbon trading landscape, as well as improving soil structure and fertility.
Previously, there had been no definitive way to prove carbon was being stored on cropping land, but a way to readily prove that carbon could be stored in stubble paddocks would add a strong argument to croppers becoming involved in ETS plans.
Many involved in no-till systems had noted with frustration that in spite of years of stubble retention, they had not been able to make meaningful progress in improving soil carbon levels.
It had generally been attributed to the dry conditions and lack of plant bulk, but Dr Kirkby said he believed nutrient levels were the key to improving carbon levels.
If Dr Kirkby’s research does prove to be on the money, there will have to be changes to accepted wisdom in terms of soil improvements.
“With green manure crops and stubble incorporation, farmers will have to be aware that the nutrients can either benefit the following crop or benefit the soil – they can’t do both.”
He said if the following crop used up the nutrients from stubble residue, then it would not be available for the microbes required to create soil carbon.
Dr Kirkby said the best way to increase soil carbon would be to incorporate stubbles, and potentially treat immediately after harvest with low rates of the N, P and S required to promote carbon growth.
“If the nutrients are there, you’d be surprised how quick the stubble can break down, even in the dry Australian summer.”
However, he acknowledged that soil carbon growth may not be the key priority for growers, depending on their soil type – particularly for those in erosion-prone areas.
“Growers will just have to weigh up what they want to do with the stubble – whether it is of more value standing and acting as a cover against erosion or whether they want to boost carbon levels.”
Written by GREGOR HEARD
Stock and Land, Page 9, November 13, 2008
Queensland Country Life, Page 9, November 13, 2008
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CSIRO scientist, Clive Kirkbyat the Hamilton Branch SFS trial site near Dunkeld where the research is underway. The research is possible through funding from theAustralian Government's Caring for Our Country initiative. |
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