Vogel and his colleagues conducted the first large-scale field study of switchgrass by monitoring its growth on the borders of 10 farms in Dakota; they noted the amount of seed, fertilizer and fuel used, the amount of precipitation and the amount of grass harvested over the span of 5 years. Using data from corn ethanol plant technologies and smaller-scale switchgrass conversion studies, Vogel estimated that an average of 60 GJ per hectare could be obtained if the switchgrass were converted into bioethanol. That impressive 540% figure compares quite favorably to the 93% return on soybean biodiesel and (measly) 25% return on corn ethanol. Emissions produced from using switchgrass bioethanol would be roughly 94% lower than those from gasoline - making it almost carbon neutral.
One of switchgrass' many benefits, Vogel explains, is that it need not take up valuable space that would otherwise be used to grow food crops; it is perfectly happy being grown on marginal cropland. The grass only needs to be planted once - after which it will provide year on returns - and has an intricate underground root system that can lock carbon in the soil. That's not to say that switchgrass lacks its own set of potential issues.
Rainer Zah at the Swiss Materials Science and Technology research institution faults current estimates for not taking into account the global warming effects of dinitrogen oxide, a very potent GHG produced during the cultivation of switchgrass. "The technology to make full use of all the carbon in switchgrass is not yet established," said Zah, pointing out that it may yet be a while before the energy yield Vogel obtained could be replicated on an industrial scale.
While Vogel acknowledges that it will be difficult to set up "large-scale field trials . . . particularly for an extended period of time in a large geographical area," he believes the 540% figure could be increased further with better land management and breeding techniques and with improvements in cellulosic ethanol production technologies.
Via ::Nature News: Prairie grass energy boost studied in the field (news website)