Sorry to be a pendant (ok not really
) but its a plow not a harrow a harrow is a substantially different type of device.
http://en.wikipedia.org/wiki/Harrow_%28tool%29 Note that while a disk harrow (
http://en.wikipedia.org/wiki/Disc_harrow) has a passing similarity of appearance to a plow the actual operation is somewhat different.
The main difference is that a plow is designed to turn the soil while the harrow type devices only "disrupt" the soil leaving the layers more or less in the same order they were in (again the disk harrow is perhaps leaning ever so slightly towards wanting to be a sort of plow).
The confusing looking part of this rig is of course the disk on the front which makes it look like some small part of a disk harrow, however its job is just to prep the way for the operational part of the plow that runs behind it.
Small correction on Dick the round disk part is spelled coulter with a u (
http://en.wikipedia.org/wiki/Coulter_%28agriculture%29) - although I could certainly see the u being dropped in parts of the US similar to how color is no longer colour.
Agree that the fork thing looks more or less homemade or maybe made to order by a small metal shop, the welds (nicely done) make it look like it was built up from maybe three pieces (there seems to be: the pipe handle, the tooth piece, and ?maybe? a bar welded between the two?). The teeth look somewhat like the teeth from some sort of clipper but seem much coarser than the ones I'm familiar with so no sure what it would have come from. Would be interesting to figure out what the teeth came from.