WITH all the posturing to provide soil carbon services and products, most of then not backed by science, farmers have been urged to hasten slowly. KIM WOODS reports

Beware the snake-oil salesmen flogging carbon credits, at least until science gets a better handle on what happens to carbon in the soil.

That was the general consensus at the recent North East Soil Carbon Forum at Wangaratta.

Victorian Department of Primary Industries policy manager David Griffin said food and fibre would remain the cake, with carbon the icing on top.

"If anyone thinks they can make a living off carbon alone, they are living in fairyland," David said.

"Some policy makers see soil carbon as low-hanging fruit for our greenhouse-gas emissions, but it's not that at all."

He said carbon policy was a "moveable feast" with no agreement on revised accounting rules for soil-based carbon at Copenhagen's climate change summit last December.

But, he said, soil carbon offsets were not off the agenda despite the carbon pollution reduction scheme being postponed until after this year's election.

The National Carbon Offset Standard is due to start on July 1, replacing the "greenhouse-friendly" standard.

Offering a revenue stream from carbon, it will "offset" greenhouse gas intensive activities such as brown coal generators.

The standard will enable voluntary off sets from this year for soil carbon, pre-1990 forestry and non-forest revegetation.

"Soil-carbon offsets are not a get rich quick scheme," David said.

"There is significant transaction costs associated with soil-carbon sink registration, measurement and monitoring and maintenance."

David told landholders to "hasten slowly" when it came to the carbon market.

"There are firms positioning themselves in the agricultural sector and soil-carbon market to provide services and products," he said. "The promotion and marketing is often based on anecdotal information, field observations and testimonials.

"These claims are not backed by science and there is limited scientific knowledge on some aspects of soil carbon."

David said a methodology for trading soil carbon was needed. "It is a case of buyer beware - if it sounds too good to be true, then it may be," he said.

CSIRO's head of soil carbon research, Jeff Baldock, told the forum said there was potential to increase the carbon content of Australian soils.

"Soil carbon can play a role in mitigating greenhouse-gas emissions but will not be the solution," Dr Baldock said. "At this stage, farmers are paid to remove carbon in food and fibre but the potential does exist to sequester carbon in Australian soils."

However, it was difficult to justify managing for soil carbon on the basis of carbon trading alone.

"Farmers should do it for all the other benefits such as improved water holding capacity, nutrient cycling, soil stabilisation and erosion protection," he said.

Dr Baldock said research had shown by increasing soil organic carbon from 1-2 per cent in the top 0-10cm of soil, water retention increased 2-5mm.

"Farmers need to understand their soils and their potential to capture carbon," Dr Baldock said. "At least 50 per cent of carbon we add to the soil is respired, so to increase soil carbon by an extra one tonne/ha a year, we will need to produce an extra 4.4 tonnes of dry matter/ha."

Dr Baldock said "carbon-friendly" practices in cropping areas could improve soil carbon levels by 0.2-0.3 tonnes per hectare each year. This included zero tillage and full stubble retention.

However, under traditional cultivation, levels could fall 0.3-0.6 tonnes per hectare each year.