Crop-derived first-generation biofuels are controversial because of their competition with food supplies and the uncertainty regarding their environmental performance. However, they are currently being used in practical applications, particularly because the second and third generation biofuels are not likely to replace them for another few years. In this study, we performed a life cycle assessment of 5 energy crops for bioethanol production in Japan to evaluate the improvements in breeding and cultivation practices. In addition, to determine the possibilities of first-generation biofuels, we analysed the contribution of different components to the crop cultivation system and the potential for improvements by constructing a regionalised database. The results showed that the introduction of yield increases are expected to significantly reduce the values for almost all evaluated environmental impact categories, together with disease-resistant varieties, direct seeding, reduced operations and the increased ratooning of sugarcane, primarily by reducing the input of materials per yield. Moreover, the results demonstrated the significance of combining multiple improvements in breeding and cultivation practices. We observed different relationships among the values between the crops under different impact categories, indicating the importance of a comprehensive assessment. A comparison between petrol and bioethanol showed unfavourable outcomes for bioethanol production and use on the environment, suggesting that further improvements are needed to ensure the potential of bioethanol production in Japan. These improvements will be accomplished by focusing on improvements in the environmental performance of particular factors such as reducing compost-derived ammonia discharge and decreasing nitrogen input through adequate fertilising. (C) 2011 Elsevier Ltd. All rights reserved.