BIOCHAR may increase crop yields, but at $5000 a tonne, farmers won't be rushing to place orders.

As a stabilised form of carbon, biochar is being touted by the scientific community as a way of lifting dryland broadacre crop production.

Biochar can be made from green waste, cereal stubble, digested sewage sludge or composted urban waste.

CSIRO Land and Water research scientist Evelyn Krull said biochar increased fertiliser efficiency by creating a habitat for beneficial soil fungi.

But, it could also reduce herbicide and pesticide efficacy, Dr Krull said.

"Biochar may work well in some soils but not others," she said.

"There is a lack of standards or certification - someone can make something black in their backyard and call it biochar."

Dr Krull is leading two national research projects on biochar.

The projects are studying the biological, chemical and physical attributes of biochar in soil and crop types.

Speaking at a Grains Research and Development Corporation update, Dr Krull said biochar improved soils by suppressing methane and nitrous oxide release.

In turn, this offset agricultural greenhouse gas emissions.

Dr Krull said trials had shown positive responses to biochar and fertiliser in semi-arid Australian soils.

"Low rates of application in an Australian study in wheat suggested that significant fertiliser savings can be obtained through biochar (applications)," Dr Krull said.

"The cost to commercial producers is $5000/tonne as it is not currently discussed by Government as a carbon sequestration tool."

Dr Krull called for long-term field experiments to study changes in biochar applications over 20-50 years.

The University of Melbourne's Dr Richard Eckard said biochar science was not well understood.

Dr Eckard, School of Land and Environment associate professor, said the economics of biochar were yet to be assessed on any significant scale.

"The carbon credit for converting organic material into a more permanent form of carbon may well be attributed to the factory where the pyrolysis (incineration) occurred," he said.

This would mean few incentives for farmers unless they were negotiated.

Dr Eckard said biochar certainly had a role to play in the storage of carbon.

But it should be seen as a complementary measure in emission reductions and not the panacea, he said.