Washington, DC - Ethanol is far from a cure-all for the US's energy problems. It is not as environmentally friendly as some supporters claim and would supply only 12 percent of the country's motoring fuel - even if every hectare of corn were used.
Researchers warn of exaggerated expectations that ethanol could dramatically change America's dependence on foreign oil by shifting motorists away from petrol; University of Minnesota researchers found that bio-diesel from soybeans is a better choice than corn-produced ethanol.
But "neither can replace much petroleum without affecting food supplies", the researchers concluded in a paper published in the Proceedings of the National Academy of Sciences.
It said development of non-food materials such as switchgrass, prairie grasses and woody plants to produce cellulosic ethanol would offer greater energy output with less environmental damage.
But creation of cellulosic ethanol remains in the laboratory research stage, and most researchers agree even non-food sources of ethanol would fall far short of replacing petrol.
Bio-fuels such as ethanol are "not a practical long-term solution" and their widespread use - even from non-food crops - could have a "devastating" impact on agriculture.
Researchers James Jordan and James Powell of the Magleve research centre at the Polytechnic university of New York wrote: "Ethanol from 120-million hectares of switchgrass still could not supply our present petrol and diesel consumption, which is projected to double by 2025.
"The agricultural effects of such a large-scale programme would be devastating."
There is concern that using corn and soybeans for ethanol would create competition for food crops and reduce soil fertility by not ploughing wastes back into the ground, but National Corn Growers Association spokesman Geoff Cooper called suggestions that the growth of ethanol would jeopardise food supplies as "fear-mongering."
He said demand for corn for livestock feed had been flat and increased production and expected higher yields per hectare would provide plenty of corn to meet all needs.
University of Minnesota researcher Jason Hill said: "We believe bio-fuels such as ethanol have a significant potential."
But he added ethanol should not be viewed as "a saviour" to America's energy problems and its rapid expansion as a motor fuel had its drawbacks, especially if it depended on food crops such as corn and soya beans.
If every hectare of corn were used for ethanol, it would replace only 12.3 percent of the petrol used in the US, Hill's study said, adding that the energy gains of corn-produced ethanol were only modest and the environmental impacts significant.
Environmental drawbacks
Corn-based ethanol was often touted as a "green", environmentally friendly fuel but its life-cycle environmental impacts were mixed. It produced only 12 percent less "greenhouse" gases than petrol and had environmental drawbacks, including "markedly greater" releases of nitrogen, phosphorous and pesticides into waterways as runoff from corn fields.
Ethanol also produced more smog-causing pollutants than petrol per unit of energy burned, the researchers said, especially at higher concentrations in petrol.
"There's a lot of green in the money that's going into ethanol but perhaps not so much green is coming out as far as the environment is concerned," Hill said.
The ethanol industry says there is little new in the University of Minnesota study.
Silver bullet
Renewable Fuels Association spokesman Matt Hartwig said: "Everybody in the industry recognises that there is a limit to how much ethanol you can produce from corn.
"Nobody is saying that ethanol is the silver bullet that is going to solve all our energy problems. It's going to take a whole host of technologies but ethanol and other bio-fuels play a very critical role."
About 14 percent of the US corn crop went to ethanol in 2005; it was 11 percent four years earlier and in 2006 could rise to 19 percent, according to US Agriculture Department estimates.
The Corn Growers' Association says that by 2015 a third of all the corn grown would probably be used for ethanol and the US Energy Department says it has a goal of 30 percent of the fuel used by motorists to be ethanol - both corn-based and cellulosic - by 2030. - Sapa-AP