Further north, the stands appear to have slow but healthy new growth. Older alfalfa stands with less than 4 alfalfa plants per square foot should either be rotated to a new crop or overseeded with something other than alfalfa to avoid autotoxicity. If perennial weeds are not abundant in an older alfalfa stand, the stand can be reseeded with a drill as soon as the ground firms up. The species you seed will depend on the anticipated future life of the stand. Red clover, orchardgrass and perennial ryegrass all will be vigorous seedlings and able to compete with established alfalfa.
Perennial ryegrass is much less likely to survive the winter.
Another option if the alfalfa is winterkilled and results in a predominately grassy field, treat it as a grass stand. Fertilizing thin grass stands with nitrogen normally produces higher yields than any attempt to interseed legumes into the stand. It is critical to initiate a grass fertilization program early in the spring season. Optimum nitrogen rates depend on the price of hay and the cost of nitrogen fertilizer. This can be determined from the table in the Field Crop Recommendations Publication 296.