I was under the impression that nitrogen-fixing crops were a good thing
until a few weeks ago I heard two farmers discussing on radio how "growing
beans makes a mess of the soil and removes the nutrients".

I'd like to know how the two things can be true. I'm aware of the
root-nodules on bean plants so they certainly do fix their own N so why
would they not be a desirable crop ?

In Japanese agriculture of the Eddo period and possibly earlier, farmers
were required by quite rigid rules to grow rice in the middle of the field
and beans around the edges to shelter it and provide the soil with nutrients
so it must work.
I don't hear about crops being combined today outside of some rotation
systems even though this method makes run-off problems non-existent.
Is it perhaps because the natural fixing-qualities of bean plants is fairly
feeble compared to present-day fertilizers?
Thanks
BG.