[northfifeduckling]

I know that legumes are great for the soil, so do I just leave peas and beans to rot on the bed over the winter or do I dig them in? Last year I cut them off at the roots. What do others do??

[BlueDaisy]

So far as I know, the nitrogenous nodules are attached to the root system so we are planning on just chopping off at the base of the stem and leaving the root system to rot down/be dug in. Putting the leaves on the compost heap.
Will be interested in any other replies to see if I'm right!

[Mo]

We just chop them off and leave the roots in, the plants go on the compost. Well, this year the pigs had the pea vines but they weren't keen on the broad beans plants, although they liked the tops earlier in the year - so do we but we sacrificed most of them. Our runners and french are still in.

[Fleecewife]

Yes, I do the same - cut them off at ground level and leave the roots to rot down in the soil.  The tops go on the compost.  Occasionally the roots (a bit like dahlia tubers) of the runners, which are in the polytunnel, come up the following year, but usually later than the ones I sow.

[smallholder in the city]

Yes the goodness is in the root nodules which convert atmospheric nitrogen to useful nitrogenous compounds that plants can use. The process is actually carried out by Rhizobium bacteria that live in the root nodules. So the roots are the important bit to leave in the soil, although letting the rest of the plant rot down or digging it in won't do any harm and will add organic matter to the soil (so long as there is no disease).

Nitrogen is one of the major plant nutrients and essential for growth so always good to put some back into the soil. 

There are other plants that do the same (mostly in the legume family) for example Bird's foot trefoil is a very pretty little native plant with bright yellow flowers, very easy to grow. I'm planning to use it as edging around some of my raised beds next year as it also attracts bees