by Bob Tippee, Editor The environmental halo over the politically angelic head of biofuels is growing a new layer of rust. Biofuels, according to early marketing, are environmentally benign because affiliated plant growth absorbs carbon dioxide enough to offset emissions from fuel combustion. But that neat cycle isn't the whole story. Meaningful production of biofuels requires expansion of agriculture, with all the land-use changes, fertilization, and irrigation that come with it. Viewed systemically, biofuels have proven not to be the environmental balms their supporters make them out to be. Now comes another environmental demerit: Crops grown as feedstocks for biofuel production c...