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.

Carl Nash
Washington, D.C.

I don’t know whether to laugh or cry when I see President Bush’s oft-cited goal of cutting gasoline usage by 20 percent in 10 years. A 20 percent reduction is available overnight by simply reestablishing a nationwide 55 mph speed limit and enforcing it with speed governors on all public road vehicles. I tested this on several road trips this summer. When I drove a maximum of 55 mph I got about 20 percent better fuel economy than when I drove near the posted speed limit. Substituting fuel production for food production doesn’t make sense to me. We just need to drive more slowly.

Bud Henderson
Knoxville, Iowa

Your story, like many I’ve read recently, argues that high-cellulose crops are a better choice than corn for producing ethanol. I suspect that millions of homeowners would cheerfully add their grass clippings and autumn leaves to the stockpile of poplar, switchgrass, and wheatgrass intended for biofuel generation.

A.C. Grover
Southbury, Conn.