Interesting post here: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=17566
A further random aside: i have no idea what alfalfa is. It seems to be a well-known plant in the US, but i don't think we have it in the UK. Sources tell me we call it 'lucerne', and we don't grow it. It seems we grow various beets and brassicas instead, plus maize and ryegrass. Perhaps because of the climate? Although perhaps just through absentmindedness:
https://www.cotswoldseeds.com/seed-info/lucerne-also-known-a...