That, and most of the other nutrients which was needed to grow the vegies ( like phosphates and potassium) are flushed into the toilet. There will be no long term permaculture without cycling those back at some point. Otherwise, organic or not, this will remains an wasteful open loop.

It isn't legumes that absorb nitrogen from air. It is bacteria that lives on their roots.

That is true but legumes actively foster those bacteria on their roots and without the legumes most of that bacteria dies. Its a symbiotic relationship.

I think that's why it's good to rotate beans or plant clover cover crop.

Three Sisters: Corn, Beans, Squash: https://en.wikipedia.org/wiki/Three_Sisters_(agriculture)

Companion planting: https://en.wikipedia.org/wiki/Companion_planting

Nitrogen fixation: https://en.wikipedia.org/wiki/Nitrogen_fixation

From https://news.ycombinator.com/item?id=43764441 :

> "Discovery of nitrogen-fixing corn variety could reduce need for added fertilizer" (2018) https://news.ycombinator.com/item?id=17721741