This article ignored important research by David Tilman and Jason Hill of the University of Minnesota. They found that planting a crop of 18 different native prairie plants grown in highly degraded and infertile soil with little fertilizer or chemicals yielded substantially more bioenergy than a single species in fertile soil. In fact, their crops substantially improved the quality of the soil and sequestered carbon to boot. Their results were published in the Dec. 8, 2006 Science (see SN: 12/9/06, p. 372). The researchers noted that resultant hay is a high-value energy source that can be converted into biofuel or mixed with coal for electricity generation.