I planted my alfalfa in early spring. It came up good but with a ton of weeds. I just cut to about 3 inches....will it come back in time for a decent ffod plot for fall?

Yes, you should be fine, assuming the weeds are in check.

Alfalfa is vigourous - and for 2-3 years it can absolutely dominate a field. - But it ihas to get established and 6.5Ph is kind if critical - If it grew well in year 1 - expect good things for Year #2 and after. It sometimes grows well with timothy, or other grasses (Bovine typeplot) - and has excellent biomass - unless you have many many deer/square mile - you'll probably need to mow it 2x per year - I would leave the clippings on - but if your soil is really fertile - removing them is OK.

Fh