They included the energy required to grow the crops, run the machinery, the cost of pesticides and fertilizers as well as the environmental impacts of the chemicals used. They added in the cost of transportation and processing required to transform the food source into ethanol.
Overall, corn yields 25% more energy than the cost to produce the fuel, while soybeans yield 93% more energy as biofuel.
Ecologist David Tillman, at the University of Minnesota in St. Paul, noted:
The goal wasn't to pick a winner or loser...Using food for biofuels has been a very good way to demonstrate that biofuels are a viable product.
The analysis noted that even if all the corn in America was converted to biofuels, only 12% of the gasoline and 6% of the diesal demand could be met.
Extracted from Science News, 15 July 2006 vol 170 p 37 by A. Cunningham.