Linc,
consider trying a small-scale soil tranfer experiment from your inoculated garden soils out to the pasture. When I was in grad school there were people workingto develop mycorrhizal and rhizobium innoculant and they have had some success. But it is noteworthy that many of the scientists (not students) believed that soil transfers were still a good way to go. Get a
bucket of the good stuff and trowel it in around a marked area of alfalfa - probably springtime is best - and see how that goes. You could scale up from there. Or it might take off if the plants are spaced tightly and a light till would move the topsoil around a bit.
I also learned that plants which are normally mycorrhizal, eg nursery grown
natives ornamentals, tend Not to form the mycorrhizal symbiosis when they are fertilized. We all assumed the plants were thinking "why bother to spend the
energy?". There was similar thinking about the n-fixing bacteria, though I don't know that I ever saw a reference. So if your pasture is rich in N from former fertilization that might explain the scarcity of nodules.
Somewhere in my mass of printed knowledge (but not in my gray matter) I must have some serious refs. I will bookmark this thread and come back to it. I studied mycorrhizae on natives in grad school. I learned (from the best) that the vast majority of wild plants form mycorrhizae. Weeds often do not, which is thought to be an adaptive strategy for success in degraded sites. There are academic citations for that. Small scale soil transfers are definitely a good idea for getting natives established in new or damaged sites. Do some little experiments, take pictures and keep notes!
Good luck to you!
Kathy J.