its an aerator spike of from a roller type aerator used to cure soil compaction. other types used would pull cores out of the ground and are used more for root aeration. the type you found can be had as long as 24 inches. ive seen these at a local irrigation shop that i get some plumbing supplies from. i think they are attached just by driving them on with a hammer as they have a slight taper to them. was it found in a vertical position? if so it would stand to reason that it pulled of from its mount. i tried to load a pic but it says that it cant load that type of file.

maybe someone can google one and get it to load. dave