The environmental impacts of biofuel crops vary considerably. Among the first — generation feedstocks (e. g. sugar cane, sugar beet, maize, cassava, wheat, oil palm, rapeseed and soya bean), some absorb more CO2 than they release. But the wider environmental costs may still be greater than the benefits. For example, rapeseed offers relatively little benefit in terms of CO2 emissions and energy dependency when its impact on land and soil is taken into account (Russi 2008). Doubts have also been raised about staple food crops. Maize, in particular, has been regarded as not producing a worthwhile amount of energy when all the inputs are taken into con­sideration (IEA 2007). That said, it is one of the more efficient (others are wheat, sugar cane and sugar beet) biofuel crops in terms of reducing in CO2 emissions. On the contrary, the production of soya bean-based biodiesel releases substantial CO2, but has been pushed in the USA in recent years when other forms of oil-rich biomass are regarded as more environment friendly for biodiesel production (Pahl 2005).

Second-generation biofuel crops such as switchgrass, alfalfa, reed canary grass, Napier grass and Bermuda grass, which are mostly perennial, have fewer environmental impacts than first-generation crops. This is because the lower fertilizer input and less-intensive farming practices that these crops require help with respect to achieving greater reductions in GHG emissions (Karp and Richter 2011). In comparison with annual crops, perennial crops can have a positive effect on environmental quality and biodiversity (Sanderson and Adler 2008). In addition, as new technologies and processes for biomass production continue to mature and lead to the commercialization of second-generation biofuels, these biocrops are likely to revolutionize the biofuel industry (Ragauskas et al. 2006). Nevertheless, the environmental costs of biofuel feedstock are mostly viewed by biofuel proponents as either insignificant because of the limited economic and ecological value of existing vegetation and land uses, or worth bearing on account of the expected future benefits (MAPA 2006).