Toward nitrogen neutral biofuel production

► Current biofuel production closes the carbon cycle but not the nitrogen cycle. ► The energy-intensive Haber-Bosch process supplies nitrogen fertilizer for feedstocks. ► Carbohydrate conversion to biofuels does not recycle nitrogen fertilizer. ► Protein to fuel conversion closes both carbon and nitrogen cycles by recycling ammonia. ► Feedstocks grown with reused ammonia lower fertilizer demand and maximize CO2 fixation.