Another thing to consider is that alfalfa may increase the organic matter in your soil and improve the soils permeability if you wanted to no till corn and beans later on in the same place. That may be something thats hard to put a pencil to though. I have a field or two that Im considering doing that with just to try and gain something for later on. I may do something other than alfalfa though. I have some fields right now that were mostly grass hay before I rented them and I have been continuosly no tilling corn and beans since I broke them out. I can see a yield advantage over similarly sloped fields I farm and also very minimal erosion compared to similar fields that havent had any hay history.