[sebsands]

 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?

[coldandwindy]

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!

[mumofstig]

The leaving of nitrogen after peas and beans is often mentioned but modern research has shown that unless the whole plant in dug into the soil, it actually makes very little difference.

When the grain from a grain legume crop is harvested, little nitrogen is returned for the following crop. Most of the nitrogen fixed during the season is removed from the field as grain. The stalks, leaves, and roots of grain legumes, such as soybeans and beans, contain about the same concentration of nitrogen as found in non-legume crop residue. In fact, the residue from a corn crop contains more nitrogen than the residue from a bean crop simply because the corn crop has more residue left after the harvest of corn.

 ...legume crop only adds significant nitrogen for the following crop if the entire biomass (stems, leaves, roots) is incorporated into the soil.... Roots and crowns add little soil nitrogen compared with the aboveground biomass.

NMSU: Nitrogen Fixation By Legumes