I plant my cover crop in mid-October. The seed mix include several types of nitrogen fixing legumes (various beans and peas, lentils), clover, oats, vetches (of several varieties) buckwheat, and a few others.
Two days before I'm going to sew the seeds, I'll dump them into a 5-gal pail and mix them with about 2 gal. of fresh rainwater or other non-chlorinated water (don't use tap-water, as the chorine will kill the bacteria in the inoculant—even 2 days later). Seed swells once it gets wet, so you can't fill your bucket all the way to the top with dry seed. Maybe fill it 2/3rds of the way full before adding water.
By the next day, all that water has been absorbed by the seed. I'll turn the seed by hand, or dump it from one bucket to another, just to make sure everything has been evenly moistened.
I'll add the inoculant to the bucket of moistened seeds the night before I'm going to sew the seeds. It's black and powdery, like black flour. I'll mix it well with the seeds and let it sit overnight.
The next day, I'll sew the seeds. Normally, I'll rake-back the wood chip mulch that covers the garden and orchard, broadcast the seeds over the bare soil, and then throw the mulch back over the seeds. This is enough soil to seed contact to assure effective germination, and it keeps the inoculated seeds from being irradiated by the UV rays of the sun. Germination is evident within a couple of days and within 2 weeks, there is a 3 inch carpet of green throughout the garden/orchard.
A month and a half later (today), the cover crop is about 12 to 18 inches high. No sunlight is reaching the soil anymore—it's a giant biological solar cell, capturing energy and transferring it to the soil below. The legumes are showing nitrogen nodulation. My chickens have been turned loose into the cover crop (from which they were excluded for the first month) and they gobble up the tender young oat plants and peck at some of the other leaves.
I'll let it grow till the second week in January, when I'll have a class of students over to the house to pull it up and build a massive compost pile. Where cover crops are growing in the raised beds, we'll use a hedge trimmer to clip them back to the surface of the soil (no till) and leave the roots in place. Otherwise, everything else gets pulled up and piled up. Some of the nitrogen nodules are left in the soil when you yank the plants out, but much of that N goes into the compost. I'm very conscious of the green to brown ratio of this compost pile, as I don't want all that N to gas-off. I'll make sure that there is plenty of dry straw and shredded paper in that hot pile. It doesn't make sense to go to all the time and expense of raising a nitrogen fixing cover crop if you're just going to yank it out of the ground and let it gas-off in a hot compost pile. I wish I could graze the cover crop down with cows, but alas, I live in the suburbs 15 minutes from Disneyland -- not exactly America's agricultural heartland.
How much of the bacterial inoculant remains in the soil from year to year? I don't risk it and assume that the correct bacteria will be there. I re-inoculate every year.
Best of luck with your experiments.