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.