"If we want to grow crops to produce biofuels, it can only be financially viable if it's done in an intensive manner," Arnaud Apoteker, spokesman for Greenpeace France, told Reuters.

"This means using a lot of imputs such as fertiliser or pesticides, some of which have a major drawback of being derived from petrol," he added.

France aims to raise biofuel incorporation in fuel to seven percent by 2010.

Apoteker said France was the world's second largest pesticide user after the United States.

"And the French use pesticides more intensively per hectare than they do in the US," he added.

Fabrice Flipo, responsible for energy campaigns at the French branch of Friends of the Earth, said biofuels consumed more energy than they actually produced, though they did release slightly less greenhouse gas emissions than ordinary fuels.

"It's a partial solution," he said.

CO2 EMISSIONS

A study carried out by France's environment institute (Ifen) and released last month shows that biodiesel used instead of standard diesel allows a 75 percent reduction in greenhouse gas emissions released during the whole of the fuel's life cycle, from production to combustion.

"The use of ethanol instead of regular gas allows a reduction of 60 percent (of greenhouse gas emissions)," Ifen said.

The study shows that the use of biofuels in 2005 should prevent the emission of 1.5 million tonnes equivalent in carbon dioxide (CO2) and the target for 2008 is a further seven million tonne reduction.

Apoteker questioned whether the study had taken account of all the inputs used in crop production.

"What do we mean exactly by the life cycle?" he said.

He said biofuel production could bring more genetically modified crops (GMO) to France, a country where public protests against them have been strong.

"The biotech industry could take advantage of the situation to sell more GMOs in France," he said.

He added that the solution to France's energy needs could not be found in one source.