beans for nitrogen - bury tops or mulch?

I am going to cut/trim my beans to get the roots to release nitrogen.  Do I bury the top portion of the plant or mulch with it?

Which is the best to take advantage of the nitrogen in the top of the plant?

The nitrogen is on the roots of the plants.  Cut the tops and mulch with them.

Ryan H wrote:
The nitrogen is on the roots of the plants.  Cut the tops and mulch with them.

No, this is a common misconception. The nitrogen is fixed in the roots but the plant  transfers most of it to leaves flowers and seeds as these form. Cutting and mulching is good

This is not actually a particularly efficient way to improve soil, but better than nothing. A dense green manure crop with legumes and non legumes is better than a legume monocultuire.

The nitrogen from the mulched legumes will inhibit more fixation so if the beans are going to continue growing it is good to use the mulch elsewhere

Depends what you mean by bury.  I avoid tilling up the soil to mix in organic matter but tucking the material under my pre-existing mulch layer works pretty well.  Then the roots will already be buried and have fixed some nitrogen while the tops also decompose and contribute their share.  In some cases I will just knock over a plant so it's like part of the mulch but not severed from the roots and proceed to plant something next to it.  This could be because something's a good companion plant, because I'm waiting for it to go to seed, or maybe just hoping for a little extra life and organic matter while the next generation of seedlings that will take up that space grow.