Sugar cane requires less fertilizer than other biofuels

Flickr/Rachel Clarke

A new paper suggests that biofuel production may be contributing to an increase in greenhouse gas emissions.

The lead author and Nobel laureate Paul Crutzen and colleagues from the United States and Europe suggest that the nitrogen fertilizer required to produce crops for biofuels may result in larger nitrous oxide emissions than previously thought.

According to the study, microorganisms turn 3–5 per cent — rather than the one per cent estimated by the Intergovernmental Panel on Climate Change — of the nitrate used for fertilizing the crops into nitrous oxide.

Nitrous oxide is one of the major greenhouse gases; when considered over a 100-year period, it has a potential to influence global warming 296 times greater than that of carbon dioxide.

The global warming caused by the nitrous oxide produced by rapeseed is 1–1.7 times more than the 'cooling' effect due to saved fossil fuel (carbon dioxide) emissions. For corn, this figure is 0.9–1.5, indicating that it is perhaps better to continue using petrol than to grow and burn biofuels.      

Sugar cane was the only crop shown to have a favourable balance of greenhouse gas savings and emissions, because it requires less fertilizer than other biofuel crops.

Brazil, one of the world's major sugar cane producers, has invested heavily in ethanol production and biofuel use. According to the Brazilian Geographic and Statistics Institute, Brazil's sugar cane production reached 425 million tonnes in 2006–2007.

Jurandir Zullo Jr, an agricultural engineer and researcher from the Brazilian Centre for Meteorological and Climate Research in Agriculture (Cepagri), says the Crutzen study is relevant, but many other factors need to be considered when calculating the greenhouse gas emissions of biofuels, from chemical to social and economical aspects.

He adds that if these conclusions were confirmed, it would encourage further sugar cane production in Brazil. The expansion of sugar cane crops however threatens to continue to encourage deforestation, which also contributes to global warming.

The discussion paper was published in Atmospheric Chemistry and Physics Discussions.

Link to full paper  [382KB]