Alfalfa indeed would produce less ethanol than corn. Even corn is not a good choice if the amount of ethanol per acre is considered, but that doesn't seem to be on the minds of decision makers these days. Alfalfa is mentioned as an alternate crop because of the positive effects that it has on the soil, replenishing it for the following crop of corn. Most of us would rather see the corn go back to food production, but perhaps the alfalfa would feed the cattle that is missing out on their usual corn-based diets. The real point is that corn is not the only source that the United States can use to generate their alcohol fuels, which are being mandated by the government.
[Source: Earth Portal via Treehugger]