Corn ethanol produces 25% more energy than is used (mostly fossil fuel) in producing it, according to new research from the University of Minnesota. However, the net energy gain is much higher, 93%, from biodiesel fuel derived from soybeans.

Most of ethanol's 25% energy dividend comes from the production of ethanol's byproduct, dried distillers grains, used mostly as animal feed.

The research finds that alternative crops such as switchgrass, which can grow on marginal land with minimal input of fossil fuel derived fertilizers and pesticides, offers the best hope for the future.

Already, 14.3% of corn grown in the United States is converted to ethanol, replacing just 1.72% of gasoline usage. Even if all the remaining corn were converted to ethanol, the total ethanol would only offset 12% of gasoline. The entire soybean crop would replace a much smaller proportion of transportation fuels - only 6% of current diesel usage, which itself amounts to a tiny fraction of gasoline usage.

The researchers examined every stage of the biofuels' production and use. They considered such costs as the effort to raise crops, environmental effects of fertilizers and pesticides, transportation and the energy required to distill ethanol.

The analysis showed that growing both corn and soybeans caused soil and water pollution from such chemicals as the nitrogen and phosphorus in fertilizer and from pesticides, with the pesticides used in corn production being especially harmful. But biodiesel used, per unit of energy gained, only 1% of the nitrogen, 8.3% of the phosphorus and 13% of the pesticide (by weight) of corn production.

The researchers also compared greenhouse gas emissions from the two biofuels with emissions caused by producing and burning enough gasoline or diesel to yield the same amount of energy. Emissions from the production and use of corn grain ethanol were 12% lower than the net emissions from gasoline; the reduction was 41% for biodiesel from soybeans. These figures show that biofuels have the potential to provide significant environmental benefits.

However, the benefits will only be substantial when much more biofuel is produced and when it has much greater greenhouse gas reductions. For example, if one replaced a total of 5% of gasoline energy with ethanol energy, greenhouse gas emissions from driving cars would be a bit more than a half percent lower (5% times 12%). It must be born in mind, too, that these figures are only for transportation-related energy usage. Considering total energy use, which includes building heating and electricity, the fraction of savings from transportation biofuels drops by two-thirds.

The researchers noted that rising gasoline and diesel prices have made the development of biofuels more economically advantageous, and that biodiesel's environmental benefits seem strong enough to merit subsidy. Yet ethanol also plays an important role as an additive by oxygenating gasoline and making it burn more cleanly.