THE future of biofuels just got brighter. Yields from farm-scale plantings of the switchgrass Panicum virgatum suggest that producing ethanol from the cellulose in these crops will be about twice as energy-efficient as previously estimated.
Researchers led by Ken Vogel of the US Agricultural Research Service in Lincoln, Nebraska, paid farmers in Nebraska, North Dakota and South Dakota to grow switchgrass for five years in plots ranging from 3 to 9 hectares. They measured the energy needed to grow the crops, including that used to make fertilisers and the diesel consumed by farmers鈥� vehicles.
From the biomass of grasses harvested, they calculated that ethanol derived from them should yield 5.4 times as much energy as all these inputs combined (Proceedings of the National Academy of Sciences, ).
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Vogel鈥檚 results will not please ecologists who want to restore prairie ecosystems by growing mixtures of grasses without fertilisers, and use the cellulose they produce to make ethanol. 鈥淚t just takes too much land,鈥� argues Vogel, who calculated that fertilised switchgrass monocultures will give higher yields per hectare.
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