I know. For simplicity, I was talking about the plants in the same generic sense that your gut microbiome is a part of you, and the dead tissues that form your hair and skin are also a part of you.

You still need to hack up the eg cereal plants so they can actually engage in that symbiotic relationship (or perhaps actually directly fix nitrogen all by themselves, without any outside help at all).

N-fixation does happen in the soil, but legumes have root nodules that host rhizobium bacteria and can assimilate the N much more easily