USDA’s Agricultural Research Service says switching to switchgrass would make sense to make ethanol. A report in this month’s ARS magazine says “this deep-rooted carbon-storing perennial has great biofuel production potential.”

This native perennial has been shown to store more soil carbon than the major U.S. farm crops. They found that switchgrass stores most of its carbon deep underground….The reason for this depth advantage lies in the fact that switchgrass has an extensive root system—with some roots as long as 8 feet—so much of the plant’s carbon is in its roots and the belowground crown tissue just above them.