Biofuels can replace a significant amount of our reliance on fossil fuels without eating into too much valuable farming land, says an Australian expert.

Prof. Robert Henry of the Bioenergy Research Institute at Southern Cross University in Lismore reports his findings in the current issue of the journal Plant Biotechnology.

"It is possible to replace oil by using a relatively small proportion of our total arable land," says Henry, who has also just completed the book Plant Resources for Food, Fuel and Conservation.

Recently, concerns have been raised about the potential for biofuel crops to take up land that could otherwise be used for producing food.

But Henry says his analysis shows the world could replace all its dependence on oil by planting 100 million hectares of prime agricultural land to biofuel crops — an area the size of Ontario, or about six per cent of the world's arable land.

He says while electric vehicles are an option in cities, liquid fuel alternatives to petrol will continue to be important for heavy transport and aviation because they have a greater energy density than batteries.

Henry says reducing consumption by increasing fuel-efficiency could reduce the area required for biofuels to perhaps plant 50 million hectares.

He says the leading biomass producers in the world include eucalyptus and sugar cane, which produce 50 to 100 tonnes of dry biomass per hectare under the best conditions.

Henry says growing biofuel crops on degraded agricultural land would be another option, although this would require more land because the productivity is lower.

He says fast-growing eucalypts have enormous potential globally as a biofuel because they have high productivity in "less than perfect environments."

But Henry says it will be important to roll out biofuel crops in a thoughtful way so that they are a genuine improvement on fossil fuels.

Today's biofuel crops only convert certain parts of the plant — such as sugar, starch or oil.

But, he says, new technology should aim to convert all of the carbon in the plant, including the woody parts, into fuel to make biofuels an efficient option.

It would also be important to consider the impact of biofuel crops on biodiversity, says Henry. Areas of high biodiversity should be locked up, while tree crops may be planted to improve the biodiversity of degraded farmlands, he says.

Biofuel crops grow quickly

Henry says another big issue to consider is that biofuel crops are generally chosen for their ability to grow quickly, and this means they can turn into weeds.

"What need to do is understand their 'weediness' before we grow them on a large scale," he says.

Henry says it's also important to consider the energy costs in biofuel production.

"The whole lifecycle assessment is important in this," he says.

This means including fertilizer use, water use and the location of biofuel crops — which would be best located in regional areas close to cities, says Henry.

"It's a challenging area because there are so many things you've got to analyse to come up with the bottom line is in terms of your net impact," he says.