"Proponents of alfalfa describe it as a wonder crop. It is self-fertilizing — fixing nitrogen from the air — and adds carbon to the soil, creating its own carbon sink and enriching the soil. Its long roots prevent erosion and improve soil and water quality...But on an energy-per-acre basis, alfalfa cannot compete with corn. USDA researchers found you could get about 137 gallons of fuel per acre for alfalfa stems, compared with about 473 gallons for corn. If farmers could also throw in corn stalks for cellulosic ethanol, that would increase corn yields to more than 600 gallons per acre — more than four times as much as alfalfa.
Alfalfa’s competitive edge could be its leaves, which are more nutritious for cattle and much higher in protein than the feed mix that is marketed as a co-product of corn ethanol. But removing leaves on a large scale is no easy task, and there is no commercial equipment currently available to do the work."