A USDOE and USDA study concluded that 50 million U.S. acres of cropland, idle cropland and cropland pasture could be converted from current uses to the production of perennial grasses, such as switchgrass, from which biomass could be harvested for use as a biofuel feedstock. Economically viable production of a perennial grass monoculture from which substantial quantities of biomass are removed annually is expected to require nitrogen fertilizer.