Friday, January 16, 2009

It's Official: Real world now 10-times faster than soil carbon models?

Models used to 'predict' the C-sequestration rates of Australian soils could be out by a fact of 6 or even 10, according to analysis of data released by the Victorian DI and GRDC recently. The data indicates that Australian soils can sequester carbon 6 to 10 times faster than the models allow.

The data was published by Dr Peter Fisher of the Victorian DPI. (Relevant sections of the press release below. Tony Lovell of Soil Carbon Australia provides the following analysis of the data:

TONY LOVELL'S ANALYSIS: "This news is still incredibly good and should really help to shift the discussion. Peter is saying the modelling suggests a 2t/ha increase in organic matter input for the same conditions, results in a change in soil carbon value of about 0.13pc after 20 years. However his research indicates that a 2t/ha increase in soil organic matter might result in approximately a 0.4pc change after only 10 years. Lets do some super basic maths on this - 0.4pc is 3 times as much as 0.13pc, and 10 years is twice as quick as 20 years - so this is still a factor of 6 times better. But what does Peter's model suggest at year 10 rather than year 20? Is the difference even greater - maybe somewhere closer to an order of magnitude (10 times)? If someone could prove to me that I could do something 6 to 10 times faster than everyone else was saying was possible, I would be a damn happy camper. And this on places where the farmers were not even focussed on building soil carbon."


A key finding from the paired paddocks trial was that for every extra tonne per hectare of above-ground and below-ground organic matter – maintained on average for 10 years, the soil carbon percentage was found to be more than 0.2% higher. 

“This increase is greater than most carbon modelling suggests,” Dr Fisher said. “Most carbon modelling indicates that increasing soil carbon is a very slow process, taking many decades to achieve significant changes. For example, modelling a 2 t/ha increase in organic matter input for the same conditions, results in a change in soil carbon value of about 0.13% after 20 years. 

“In contrast, the relationship developed between change in organic matter input and change in soil carbon at the 13 paired paddocks in the trial, suggested that a 2 t/ha increase in soil organic matter might result in approximately a 0.4% change in carbon level, after only 10 years.” 


1. Was that a 2% increase over 10 years (ie. 0.2%/yr for 10 years) or was it 0.2% over 10 years?

2. What were the land management techniques used to return the organic matter to the soil?Stubble? Stubble processed through animals? Stubble ploughed in? Compost? Each of these will have a different effect on carbon scores, depending on the availability of the organic matter to the microbes. And the state of health of the microbial community will affect the incorporation of the organic matter. Highly active soil will see stubble disappear in a few days. Inactive 'dead' soil will have stubble oxidise, with very little being incorporated. This would affect your carbon readings.

3. What other management techniques were in use on the paddocks? Cover crop? Fertiliser? Pesticides? Herbicides? Minimum Till? No Till?

4. What was the history of the paddocks? (Ie. a paddock which had been under perennial pasture until recently would be in the early stages of rapidly losing significant carbon while a long-cropped paddock would have plateaued at a low carbon point.

5. The models: how old is the data on which they were built?

6. Given what we know about microbial communities and their frontline role in manufacturing carbon, was there any analysis done of the paddocks to ascertain their background level of microbial activity before the trials commenced.

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