The nodules in the roots are the happy little homes that the plant provides for the bacteria to grow and reproduce in.

It’s the production location, not the storage location. The nitrogen is incorporated into proteins and used all over the plant. It’s especially concentrated in legume seeds.

For example winter peas can produce up to 400lbs/acre of nitrogen during its growing season (newer varieties like Icicles etc). If you removed the top and the seeds you remove around 350-375lbs of N. So you get 25-50lns of N per acre if you leave just the roots. So it’s best to incorporate the entire plant in when the seeds reach soft dough stage.