This is what is already there. There are also many ways to increase the quality and quantity of what is grown. If the forage field is dead, then you may want to bring it into your crop rotation and seed down another field ahead of schedule. If seeding down, you should select a field that has good weed control and one where you can make a good seedbed. Check the herbicide use history in the field before planting alfalfa.
Herbicides can have replanting restrictions.
If you breakup a hayfield and reseed it in the spring, you run the risk of autotoxicity from any existing alfalfa plants. This means that they won't let the new seed germinate. A rule of thumb is three weeks dead, before you try to re-establish alfalfa. It is also hard to make a good seedbed and to get adequate weed control in fields where alfalfa is recently killed and the field spring plowed. Annual forages can be an option to produce dry matter tonnage.