6. Energy and CO₂ Balance:

Other Environment Considerations

Compared with other bioenergy options, miscanthus appears to fall midway between annual crops (e.g., rapeseed, beet) and woody perennials (e.g., willow, poplar) in terms of its life-cycle analysis. If high yields can be attained, its energy and carbon balance may be favorable (though not as good as woody crops), and nitrous oxide emissions are low compared with other annually harvested crops because of its high nutrient-use efficiency (Kaltschmitt et al. 1996; Lambert et al. 1996). However, energy balance modeling has suggested that overall energy output/input ratio may be as low as 1.1 in the case of co-firing miscanthus with coal because of the high energy requirement for fuel pulverization. In the best case (small-scale heat and power cogeneration with fluidized-bed gasification/gas-turbine technology) the energy balance was 9.6 (Molenaar et al. 1996; Venturi et al.1998). Miscanthus stands also contain more large animals (mammals, birds) than other herbaceous crops (corn or reeds), possibly because of the greater diversity of canopy structure leading to a higher number and greater range of ecological niches (Jodl et al. 1998). N₂O emissions from normal levels of N-fertilizer application had only a modest effect on net offsets of greenhouse gas warming potential (6% of total CO₂ displacement) (Jorgensen and Jorgensen 1996). Some soil erosion benefits are claimed, but details are not available (Walsh and McCarthy 1998). To date, there are no reports of plant diseases significantly limiting production, but the crop is known to be susceptible to Fusarium blight and Barley Yellow Dwarf Luteovirus (Walsh and McCarthy 1998); as with other clonal crop stands, disease may present a significant risk. The European Miscanthus Improvement project has recommended that new genotypes should be sterile (e.g., triploid) as a precaution against them becoming weeds. There have been some small-scale escapes of fertile ornamental genotypes in Ohio and Indiana which have caused local concern and reinforce the case for releasing only sterile hybrids of miscanthus in the United States (D. Bergdorf, personal communication). It will be necessary to determine whether the likely benefits of miscanthus clearly outweigh any potential harm as an invasive species and to take measures to minimize the risk of harm before U.S. federal funds can be used to develop the species as an energy crop [White House, 1999; Section 2 (3)].