Re: First time Alfalfa?
Since the alfalfa is being cut for hay, the timing of the hay harvest may affect the amount of nectar that bees can harvest from alfalfa. If the alfalfa was being grow for seed, then it offers lots of nectar, but hay perhaps not.
If your farmer was interested in your bees for pollination, you should read the "Alfalfa and bees" section of this page:
You may be interested in this older thread:
USDA Zone 7a - elevation 1400 ft