By Anna Salleh for ABC Science Online, Mon Sep 22, 2008 11:36am AEST

Using waste stubble would avoid having to allocate precious food-producing land to the production of biofuels (CSIRO)

Australian researchers say biofuels made from the stubble left over from harvesting grains could replace around one fifth of the volume of petrol used in Australia.

Dr Michael Dunlop of CSIRO Sustainable Ecosystems in Canberra and colleagues will report their findings at the Australian Society of Agronomy Conference in Adelaide this week.

Dr Dunlop says based on 2001 figures, the 10 main grain crops of Australia produce about 65 million tonnes of stubble.

He says much of this needs to be left in the ground to protect soil, retain soil carbon and reduce evaporation.

This would leave just under 15 million tonnes of remaining stubble to be distributed in a way that is economically viable to collect.

"That would be equivalent to roughly 20 per cent of the volume of the petrol that we use," Dr Dunlop said.

The researchers analysed figures for wheat, barley, canola, lupins, oats, sorghum, triticale, field peas and chick peas in their study.

"[Stubble] is probably one of the more widely distributed feedstocks that is currently available," Dr Dunlop said.

He says while using waste stubble could help minimise extra energy used because the energy has already been put in to growing the grain, energy will be required to process the stubble into biofuel.

"So the quoted 20 per cent is not 20 per cent more energy to burn, [there's] no free lunch," he said.

Dr Dunlop says the amount of stubble available will vary between four and 40 million tonnes depending on how much is produced, how much needs to be retained for soil health, as well as a range of economic and technical factors.

No competition

He says using waste stubble would also avoid having to allocate precious food-producing land to produce biofuels.

And using it would also avoid having to introduce exotic and potentially weedy species.

"It's a resource that is there so we don't need to undertake any land use change in order to produce it," Dr Dunlop said.

He also says using stubble as a feedstock would not require massive additional infrastructure.

"The infrastructure required for harvesting, collecting and distributing it is all pretty similar to that used for grains," he said.

Technical challenges

Dr Dunlop says first generation feedstocks are based on starch, oil or sugar and these are more easily converted to biofuel.

But he says stubble is known as a second generation feedstock because it is a woody material and is more complicated to process into biofuel.

He says the processing technology exists, but is currently expensive because it is not widely distributed.

The stubble can be broken down by a number of means including enzymes, heat and pressure, says Dunlop.

The researchers are also evaluating other possible biomass feedstocks such as forestry residues and mallee crops.