Napier grass and Erianthus were selected as law material crops for cellulosic bioethanol production mainly due to their high biomass production and high tolerance to environmental stresses. They should be grown in non-arable lands of tropical or subtropical areas including Indonesia to avoid possible competition between food and energy production. Because their shoot biomass will be huge, production system is required to be sustainable. Root system biomass and root exudates must be examined from the viewpoint of element cycle in soil to establish sustainable production system of law material crops.