Energy Crops for Sustainable Bioethanol Production; Which, Where and How?

Bioethanol is gathering attention as a countermeasure to global warming and as an alternative energy for gasoline. Meanwhile, due to the synchronous increase in bioethanol production and grain prices, the food-fuel competition has become a public issue. It is necessary to see the issue objectively and to recognize that the real background is the change in allocation of limited resources such as farmland and water. In this review, we discuss which, where and how energy crops should be grown to establish a sustainable bioethanol production system. Several combinations of crops, areas and cultivation methods are recommended as a result of a survey of the bioethanol production system with various energy crops. In tropical and subtropical regions, sugarcane can be grown in agricultural and/or unused favorable lands. In other regions, cellulosic energy crops can be grown in abandoned and marginal lands, including lands contaminated with inorganic pollutant like heavy metals and some detrimental minerals. There also is the possibility that, for Japan and other Asian countries, rice can be grown as an energy crop in unused lowland paddy field. Regarding cultivation way, energy saving is beneficial for bioethanol production systems irrespective of energy efficiency. On the other hand, effective energy input should be considered for the systems with higher energy efficiency when available land area is limited. Exploring and developing new energy crops and varieties, which show higher biomass productivity and stress tolerances under marginal conditions, are necessary for sustainable bioethanol production because energy crop production would be restricted mostly to marginal areas in future.