it's got the juice

You're leaving out a whole sister

This just got way kinkier. And I'm into it.

That nitrogen isn't really made available unless the plant has been turned into the soil as green manure at flower. Harvesting the bean crop (protein/nitrogen rich itself) leaves the soil about neutral, maybe somewhat depleted depending on how the field is cleared and prepped for the next planting. Also, there's research showing that some corn can fix some nitrogen itself on the slimy exudates of aerial roots.

The whole three sisters thing was an early crop rotation method. Not all together like as advertised.
Beans where grown first as they are shallow rooted and produce about 50% of the nitrogen they need. If they harvest 25% of the crop and till under the rest they have around around a 25% increase in a available N.
The next season is corn and pumpkins together. They are both heavy N feeders. They spaced out the corn a lot more than modern hybrids so the pumpkins had plenty of room to grow and shade out weeds. They unfortunately share the pest of cucumber beetle species (corn rootworm).
The next season they had to go back to beans to break the rootworm cycle.
Eventually other nutrients would become low (P,K, micros etc). Other pests and diseases would buildup. They would rotate onto new plots letting the old plots go fallow for a while.
- Hm. Maybe I need to dig into the Wikipedia sources then because something is amiss here.
  https://en.m.wikipedia.org/wiki/Three_Sisters_(agriculture)
nitrogen isn't made available
You're describing N balance rather than the fixation and conversion of fixed N.
If it's fixed, it becomes plant available, by being quickly turned into ingorganic forms (primarily No3).
- That nitrogen is fixed inside root nodules on the root system of the bean plants. It's taken up by them immediately. It's not available to the corn or anything else growing nearby.
  And, you misquoted me.

Pumpkin is there to watch the action and to suppress weeds

Pumpkin is the bouncer at the corn and bean club
- Yeah it even stabs unwanted pests. You really need the squash in there to run interference on this public display of agricultural debauchery.

Also corn:

https://news.wisc.edu/corn-that-acquires-its-own-nitrogen-identified-reducing-need-for-fertilizer/

the metaphorical corn's hand

It's got what plants crave!

Very Indiana meme

i have a friend in rural Indiana who was just complaining about corn 😆
- I'll take corn over beans. Helps disguise the fact there is absolutely no geography or things to look at whatsoever in this state

Lemme tell ya all about it