Do I have to inoculate lupins?

Hi, I am planning on sowing lupine in the area where neither other legumes nor wild lupine grew before. The soil will be/is well amended, acidic and on the steep slope of the woody edge. It's clay-ish(?) I think. I want them to fix the nitrogen there and stabilize the slope (I will have other plants there as well).
Do I absolutely have to inoculate the seeds with lupine specific rhizobium to have them grow and flower this year? I have two kinds of lupine seeds, perennial blue ones and multicolored annuals.

The safe bet would be go ahead and inoculate; all the literature I can find suggests this is necessary unless the right rhizobium is already there, and that it only hangs around a few years after Lupine was last present...

However, the rhizobium/nodules are specifically needed to provide nitrogen fixation. Will the plants survive and flower without the ability to fix nitrogen? My expectation would be that some would make it, but in lesser numbers... and they won't be doing the job that you wanted them to, in any case.

I take your seeds are definitely not rhizocoated?

One option would be to go ahead and sow, then dig some up and look for nodules, in case you're fortunate and there was in fact some wild lupine around recently, and thus the rhizobium is present.

No, they aren't coated and there weren't much growing on that slope - I chopped down a few Norway maples there last fall. If I inoculate them (lupins, not maples, heh) I should do so after I scratch-ify/soak-iefy them, right? And, is it OK to still grow it in the tray or do I have to do direct sowing only? I wanted to start some seeds indoors to maximize the outcome. Since Lupine is a wild flower, how do they go about inoculation in the wild? And, lupins supposed to be flowers that thrive in poor soils so why so many gardening sites recommend composting and mulching? Beats me.
Btw, the inoculant is pretty expensive

I would guess that since the soil in the trays would be going with the lupins when transplanted, starting indoors would be fine.

Apparently there are multiple forms the inoculant can come in, which would determine how it should be applied; hopefully it comes with instructions. Expect you're right that inoculating after any other prep is done would be best, so as to not wash it right back off; if your inoculant can be applied as a liquid that might kill 2 birds with 1 stone.

As far as inoculation in the wild, this abstract suggests that, at least for those sorts, the rhizobium spread on their own through the soil... very slowly, and mostly downhill. http://www.sciencedirect.com/science/article/pii/003807179390200U

This would imply to me that transplanting Lupins which had previously been inoculated would be a good way to help spread the rhizobium around, and thus make life easier for any volunteer lupin.

Thank you, Dillon! I bought the inoculant from Hancock Seed. It is good for blue lupine only but I will do the Russell mix in it as well and see if it develops any nodules.