Having just spent the afternoon (gratefully) digging into my neighbours' pile of muck from their stables, I cannot but think that someone will want yours. A sign by the road-side, cheap local ad' or web ad' (e.g. shpock, gumtree etc) might do the trick, if you haven't tried already.
[Unfortunately, the well rotted horse manure I really want right now is right at the back of the pile - many hours of lifting and shifting still to come before I get there, but, heh!, it's free.]