Did you know that alfalfa grown is a nitrogen fixer and great as ground cover to smother weeds/be a green manure that can be turned over before it flowers?
If you are not in the season/mood to grow alfalfa, do what I do, use alfalfa pellets! It has a good all around mix of nutrients, its NPK being: 2-2-2 and you you know it won't burn your plants when it's that low.
The pellets can be purchased at local farm or Tractor Supply Stores, or you can potentially get them as rabbit pellets in pet stores, but as I don't have a bunny, I don't know the price and can only imagine that it's super jacked up.
(this is the cheap, available brand I use, about $11/50lb bag here)
(closeup of the nutrition content, more for animals though, just in case you were curious)Mostly I use the alfalfa for mulch, either by spreading the pellets straight onto or into if you so wish, the garden where they will break up in the rain, or even better, I soak them in a bucket of water and walk away for a while doing garden-y things until I walk back and they're all swollen up and easy to break apart where I spread them as nice as I can. You can also wait even longer and let them go overnight in a wheelbarrow (just hope it doesn't get rusty!) and allow the pellets to completely fall apart into strands and then toss it and the water evenly all over the garden to spread the goodness.
This type of mulching I find is immensely cheaper than regular mulch by the bag due to alfalfa's compressed nature. The alfalfa releases nitrogen slowly and allows water through easily all the while breaking down into the soil well and the earthworms love it, dragging it below!
Oddly enough, my dog loves alfalfa too (part horse? or bunny? She does love carrots...) and so that may be a thought if you have a canine in your life and garden, or it could just be that my dog is a freak, which is likely.
Also, another good use for your 50lb bag of alfalfa might be to make it into tea. I have done a rather weak version of this myself, not getting into it too extensively yet, some recipes:
http://feverishthoughts.com/garden/2006/08/05/stinking-brew-alfalfa-tea/
http://davesgarden.com/guides/terms/go/2294/
Note that its best to use in spring or during summer, not in fall when you want to allow your plants to start preparing for dormancy rather get a mass of nutrients and push out fresh tender growth just before the cold hits.
Other good uses for alfalfa is that it can be as a compost activator. Break it up a bit before dumping it in your compost pile to get things hot. (More on compost activators in a later posting because it could definitely be talked about.)
Remember, alfalfa is SMELLY. I personally like the grassiness, but if you aren't a musty barnyard person, you might not like it.
Please note too that be careful when you handle it, it might have fine dust particles, so take caution to not breathe it in so wear a mask or bandana around your nose/mouth when handling!
(And when you're done with the bag, you can open it up and use it like a curtain to hide your immense of garden stuff in recycled fashion shame! ;)
