http://www.wired.com/autopia/2011/01/study-weve-got-plenty-of-land-for-biofuels/Researchers at University of Illinois Urbana-Champaign have found that biofuel crops cultivated on land unsuitable for food crops could produce as much as half the world’s current fuel consumption without adverse impact on food crops or pastureland.
The study, published in Environmental Science and Technology, identifies land around the world that is unsuitable for food production but could be used to raise biofuel feedstocks like switchgrass.
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From there they considered marginal grassland, where a variety of plants called low-impact high-diversity perennial grasses could be raised. Although such crops have lower yield than more common feedstocks like switchgrass, they have less environmental impact. Including such lands and crops nearly doubled the available land. That, they say, is enough to meet as much as 56 percent of the world’s current liquid-fuel consumption.
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Actually, they concluded a biofuel production meeting a range of from 26% to 56% of the World's liguid fuel demand was possible.