If where you are thinking of planting already has grains and other grasses, I would suggest Hairy Vetch. It will climb the stalks of grass and blooms very well and bees love it.
I have a couple acres of pasture grass/grains, and this is what I'm going to plant. It will not be crowded out by the grasses, which can happen with other low growing legumes. Keep in mind i say this because I had pasture grasses and grains that were close to 5 feet tall this year and it crowded out the other things i've planted for the bees. This year it's going to be hairy vetch sowed after the first fall rain.
20+ years with bees and still learning. Currently near Marysville, CA, 95901