For making ethanol, switchgrass appears to be a feasible choice—and a better one than corn. Working with the U.S. Department of Agriculture, farmers grew and monitored the native North American perennial, which often naturally grows on the borders of croplands. Specifically, they tracked the seed used to establish the plant, the fertilizer used to boost its growth, the fuel consumed to farm it and the overall rainfall that the areas received. The five-year study showed that switchgrass grown on plots three to nine hectares in size would yield from 5.2 to 11.1 metric tons of grass bales per hectare, depending on rainfall. If processed by appropriate biorefineries (now being built), the yields would have delivered 540 percent more energy than was used to produce them, compared with the at most 25 percent more energy returned by corn-based ethanol. The January 15 Proceedings of the National Academy of Sciences USA has the findings.
This article was originally published with the title "Better Ethanol through Grass" in Scientific American 298, 3, 30 (March 2008)