"Blooming Prairies: Whether ethanol made from cellulosic biomass is good or bad for the environment, however, depends on what kind of biomass it is and how it is grown.
In a series of tests, Tilman grew a mixture of native prairie grasses (including switchgrass) in some of the field’s plots and single species in others. The results show that a diverse mix of grasses, even grown in extremely infertile soil, "could be a valuable source of biofuels," he says. "You could make more ethanol from an acre [of the mixed grasses] than you could from an acre of corn." Better yet, in a paper published in Science, Tilman showed that the prairie grasses could be used to make ethanol that is "carbon negative": the grasses might consume and store more carbon dioxide than is released by producing and burning the fuel made from them." "