Hmmm...if it is a polearm head, I'd vote for a pike. The triangular/leaf-shape was the earlier form pre-1750 (the later ones found in Rev War-era America had sockets like this and doubled as "trench spears". Likewise, colonial Spanish polearms had sockets as this often without even a hole to secure it to the haft. Langets were not a requirement on pike heads despite popular opinion ). Later pikes had the 4-sided spike type end.
www.liveauctioneers.com/item/7784984
The widened end of the socket bothers me a bit, though. Never seen one like that. With a sharpened flat blade, though, I don't see it being just a fence post. Still, there are other types with a widened base to consider, I guess, such as these spears-
http://en.wikipedia.org/wiki/File
ervish,_1913.jpg
A Tibetan dung-
http://ep.yimg.com/ca/I/yhst-9793451..._2074_37529329