Should corn and soybeans be used as fuel crops at all? Soybeans and especially corn are row crops that contribute to soil erosion and water pollution and require large amounts of fertilizer, pesticides, and fuel to grow, harvest, and dry. They are the major cause of nitrogen runoff—the harmful leakage of nitrogen from fields when it rains—of the type that has created the so-called dead zone in the Gulf of Mexico, an ocean area the size of New Jersey that has so little oxygen it can barely support life. In the US, corn and soybeans are typically planted in rotation, because soybeans add nitrogen to the soil, which corn needs to grow. But as corn increasingly displaces soybeans as a main source of ethanol, it will be cropped continuously, which will require major increases in nitrogen fertilizer and aggravate the nitrogen runoff problem.
Nor is corn-based ethanol very fuel-efficient. Debates over the “net-energy balance” of biofuels and gasoline—the ratio between the energy they produce and the energy needed to produce them—have raged for decades. For now, corn-based ethanol appears to be favored over gasoline, and biodiesel over petroleum diesel—but not by much. Similar results emerge when biofuels are compared with gasoline using other indices of environmental impact, such as greenhouse gas emissions. Another point of comparison is greenhouse gas emissions per mile driven, which takes account of relative fuel efficiency. In short, the “green” virtues of ethanol and biodiesel are modest when these fuels are made from corn and soybeans, which are energy-intensive, highly polluting row crops.
The benefits of biofuels are greater when plants other than corn or oils from sources other than soybeans are used. Ethanol made entirely from cellulose (which is found in trees, grasses, and other plants) has an energy ratio between 5 and 6 and emits 82 to 85 percent less greenhouse gases than does gasoline. As corn grows scarcer and more expensive, many are betting that the ethanol industry will increasingly turn to grasses, trees, and residues from field crops, such as wheat and rice straw and cornstalks. Grasses and trees can be grown on land poorly suited to food crops or in climates hostile to corn and soybeans. Recent breakthroughs in enzyme and gasification technologies have made it easier to break down cellulose in woody plants and straw. Field experiments suggest that grassland perennials could become a promising source of biofuel in the future.
For now, however, the costs of harvesting, transporting, and converting such plant matters are high, which means that cellulose-based ethanol is not yet commercially viable when compared with the economies of scale of current corn-based production. One ethanol plant manager in the Midwest has calculated that fueling an ethanol plant with switchgrass, a much-discussed alternative, would require delivering a semitrailer truckload of the grass every six minutes, 24 hours a day. The logistical difficulties and the costs of converting cellulose into fuel, combined with the subsidies and politics currently favoring the use of corn and soybeans, make it unrealistic to expect cellulose-based ethanol to become a solution within the next decade. Until it is, relying more on sugar cane to produce ethanol in tropical countries would be more efficient than using corn and would not involve using a staple food.
The future can be brighter if the right steps are taken now. Limiting US dependence on fossil fuels requires a comprehensive energy-conservation program. Rather than promoting more mandates, tax breaks, and subsidies for biofuels, the US government should make a major commitment to substantially increasing energy efficiency in vehicles, homes, and factories; promoting alternative sources of energy, such as solar and wind power; and investing in research to improve agricultural productivity and raise the efficiency of fuels derived from cellulose. Washington’s fixation on corn-based ethanol has distorted the national agenda and diverted its attention from developing a broad and balanced strategy. In March, the US Energy Department announced that it would invest up to $385 million in six biorefineries designed to convert cellulose into ethanol. That is a promising step in the right direction.
