Field beans apparently add nitrogen to the soil via their roots. Broad beans also?. Ive just read that peas add nutrients all from leaving the root system in the ground after harvsting.
Are there any othe vegetable roots that can be left for adding nutrients?
All legumes have nodules on the roots that collect nitrogen. Actually the amount of benefit depends on temperature - in a cold place there are only a few nodules when you look.
Theoretically any roots left in would have some nutrients to return to the soil but there would be a down side for many, especially those with disease related reason for wanting to clear them out & wait a few years before planting the same thing in a place . So definitely not a good idea with brassicas or potatoes.
I have my legumes growing together. When they're finished cropping I remove any supports, walk about a bit until they're all bent over, then cover in weed membrane for the winter. Next spring I put compost on top & plant the row crops into it. Seems to work!