Legumes are good for the soil in mixed plant communities. However when planting, most emphasis should be placed on legume diversity (both specie and variety) so a wide and deep base of rhizobia bacteria is built into the soil microbiology. Just because soil has a lot of rhizobia does not mean they are of the right specie for the seed you plant....so may not get favorable N capture. ABM microbials now has a 'cover crop inoculant' which contains many rhizobia species.....graphite base (lubricates drill feeds too).....no-brainer purchase IMO.
Berseem, Persian and birdsfoot trefoil should accompany several alfalfa varieties in a plot...IMO.....less pest issues, similar growth habit and maturity, and good insurance policy against alfalfa stand loss. Persian was doing extremely well on a ranch I visited in AL in June.....Petcher wants more for the seed than I am willing to pay for an annual. Trying to source it out of Oregon for next year at less cost.
I like and have grown alfalfa....still have sparse survivors....but I dislike the degree of additional management to keep the stand persistent and pure. Now, I just supply diverse seed and let nature sort out the winners! I like easy keeper plants just as well as easy keeper cows! Simple works...free native legumes work too!