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CHICAGO, July 12 — Biodiesel produced from soybeans produces more usable energy and reduces greenhouse gases more than corn-based ethanol, making it more deserving of subsidies, according to a study being published this month in The Proceedings of the National Academy of Sciences.
The study, done by researchers at the University of Minnesota and at St. Olaf College in Northfield, Minn., points to the environmental benefits of the biodiesel over ethanol made from corn, stating that ethanol provides 25 percent more energy a gallon than is required for its production, while soybean biodiesel generates 93 percent more energy.
The study’s authors also found that ethanol, in its production and consumption, reduces greenhouse gas emissions by 12 percent, compared with fossil fuels. Biodiesel, they said, reduces such emissions 41 percent, compared with fossil fuels.
The study concludes that the future of replacing oil and gas lies with cellulosic ethanol produced from low-cost materials like switch grass or wheat straw, if it is grown on agriculturally marginal land or from waste plant material.
Indeed, the study published by the National Academy of Sciences found that neither ethanol nor biodiesel can replace much petroleum without having an impact on food supply. If all American corn and soybean production were dedicated to biofuels, that fuel would replace only 12 percent of gas demand and 6 percent of diesel demand, the study notes.
Researchers at universities and at the United States Agriculture Department have debated ethanol’s benefits as policy makers continue to struggle with how to respond to high gasoline prices and how to reduce America’s dependence on foreign oil.
Some lawmakers have urged an end to federal subsidies of 51 cents a gallon for ethanol refiners. The subsidies have helped create a boom in ethanol production and have made ethanol more profitable than ever.
The researchers in the latest study question ethanol’s environmental benefits, noting that despite the 12 percent reduction in greenhouse gases, ethanol has “greater environmental and human health impacts because of increased release of five air pollutants and nitrate, nitrite and pesticides.”
Neither biofuel was cost-competitive in 2005 without subsidies. Biodiesel cost 55 cents a liter to produce, or 20 percent more than ethanol. Wholesale gasoline prices in 2005 averaged 44 cents a liter, or 4 percent less a liter to produce than ethanol, the study said. Still, biodiesel receives a subsidy that is 45 percent greater a liter than ethanol.
Analysts agreed with the study’s conclusion that biodiesel compares favorably with ethanol from an environmental standpoint. “Biodiesel is much cleaner-burning fuel and much less harmful to the environment,” Daniel W. Basse, president of AgResource in Chicago, an economic forecasting firm, said Wednesday.
But Mr. Basse said ethanol production is far more efficient, with some 420 gallons of ethanol produced per acre of corn versus only 60 gallons of biodiesel per acre of soybeans. If biodiesel use ever increased greatly, Mr. Basse said, the cost of soybean oil would rise significantly.
Brent Erickson, executive vice president of the Biotechnology Industry Organization, based in Washington, agreed that biodiesel’s potential was limited. “If you look at the amount of biodiesel you can produce, it is a drop in the bucket compared to the amount of cellulosic ethanol that could be produced one day,” he said.
The Minnesota researchers write that with a projected doubling of global demand for food within 50 years and an even greater expected increase in demand for transportation fuels, “there is a great need for renewable energy supplies that do not cause significant harm and do not compete with food supply.”