Criticised by some soil carbon advocates for being stuck in the past, scientists are embracing the present by including some less mainstream land management techniques in a three-year assessment of soil carbon potential.
The national Soil Carbon Research Program (SCRP), funded by the Federal Department of Agriculture, Forestry and Fisheries (DAFF) and GRDC, aims to define the influence of various management practices on soil carbon levels.
As well as conventional practices, the program is assessing rotational grazing and pasture cropping systems in NSW, and the performance of perennial plants in Western Australia’s traditionally annual-based pasture systems.
Soil carbon advocates like Carbon Farmers of Australia have condemned the scope of past scientific assessments of soil carbon potential.
The critics say that many conventional management systems are likely to either degrade soil in the long term, or merely maintain the status quo, which is why an increasing number of landholders are experimenting with different management systems.
Co-ordinator of the SCRP, CSIRO soil scientist Jeff Baldock, acknowledges that to date, scientific reviews of soil carbon have neglected certain management techniques.
“Some of the systems that are newer haven’t had papers written about them in the scientific literature, and they haven’t got into to the reports and reviews that we write,” said Dr Baldock, who spoke about SCRP at the 19th World Congress of Soil Science in Brisbane this week.
“But we’re trying to be as inclusive as possible in the Soil Carbon Research Program.
“We won’t get everybody, I’m sure of that, but we’re trying to get to some of these new management practices. And if we start to see benefits, or it pans out the way that some people are suggesting, maybe a Phase Two of the project - if such a thing exists - will be broader.”
For farm productivity, the form of carbon measured in different management systems will be even more important than gross quantities.
At one end of the scale, carbon is present in crop residue on top of the soil, but this contains very little nutrient. At the other end, humus contains high levels of carbon and also of nutrient.
Part of the SCRP will investigate the relationships between different forms of soil carbon and farm productivity.
“Right now, we know the links exists but we don’t have the quantitative relationships to drive a model with,” Dr Baldock said.
He remains cautious about the potential for soil carbon to become a widely tradeable commodity.
He observed that a dryland wheat farmer operating at 50 per cent water use efficiency might lift water use efficiency to 100 per cent, grow bigger plants, and leave more carbon in the soil.
But a farmer already operating at peak productivity may not be able to make meaningful increases in soil carbon within the system they are already using, Dr Baldock said.
“If they wanted to chase increased soil carbon, they may have to shift their farming system towards a system that leaves more carbon behind. Then you have to do assessments on the economic viability of that shift and other things: what’s the value of carbon, what’s the value of the product, will the soil response be enough to warrant the shift?
“I would say at this point that soils have a role to play (in carbon sequestration), but they are not the solution.”
The SCRP is due to finish in two years, but Dr Baldock hopes that progress reports will be delivered before then.
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