[QUOTE=horsepoor;8100898]
Uh, I can’t agree with this figure at all. My bins are 4’ deep (tall). By this calculation, my bin full of manure should reduce from a 4’ tall pile to 4"? Maybe if I left it there for years! Our best guess is that the piles maybe go down to about half the original size once fully composted, and even that might be optimistic. I would be wary of presenting that kind of overly optimistic figure.[/QUOTE]
IME:
Manure in a compost pile is not terribly heavy, and does not self-compact quickly. If you turn it over a few times, say weekly, I find it becomes less than half of the original size and digests well. If you turn it over weekly again for a second month, it compacts to half again. The amount of hay / shavings has much to do with it.
I agree that getting to 1/12th the volume would take some doing in the form of a pile, but I could believe that a foot thick pile of compost would add only 1" of height to the topsoil by the following season.