Could this have been used like a tobacco-cutting knife? The extended bar would have allowed for more of a swing to cut corn stalks, sugar cane, tobacco leaves (which are surprisingly thick and a pain to cut, I'm told). Just a guess-

If you google tobacco knives, you'll see all the weird shapes they came in, some for specialty removal. Here's a site for various agricultural knives and their odd shapes-
www.okapisa.com/site/awdep.asp?depnum=50598