I think we need to keep in mind that we're not having to do the work of an 8 row tractor.
We're talking about the work of 1 horse power. I've been checking out the various sizes
of power cable. They come in all sizes and I think the smallest is between 1/4th and
3/8th inch. I think a single pulley attached to the plow stringing the cable from the spool
through the plow pulley and back to the movable frame and anchored is all that would be
needed, especially adding the gearing of the differential. Cable in very long continuous
pieces will be available laying on the ground from downed power lines, which are
aluminum stranded cable of various diameters.
To pull it along the row, I envision a large wood spool salvaged from a power company, phone company, cable company, etc. about 3 feet in diameter. This would be mounted vertically on a pole (cut from a common power line pole) sunk 5 feet in the ground - deep as a common post hole digger will go, and about 5 feet above ground. It would have 4, 3" diameter by 6' wood pieces attached to the "top" of the spool. These would be used by 4 people who would walk in a circle around the spool pushing the attached "push poles", turning the spool. One person would operate the plow. That makes 4 people-power to pull the plow. If one just adds one pulley, that makes the equivalent of 8-people power. A 2 spool pulley would be 16 people-power, etc.. I think that would certainly do it.
If one mounted the spool in the center of one end of the field and placed a pole permanently at the end of each row, by attaching another single pulley to the pole at the end of the row being plowed, the main "working" spot need not change - just move the "row" pulley to the next pole when starting the next row. With an identical setup at the other end of the field, you would need 8 "walkers" instead of 4; but the total number of people required to work a field would still only be 9. While one group works, the other group of 4 rests. The plow would stay attached to both sets of pulleys, so that when it reaches one end of the field, the other pulley has been "unspooled" and is ready to pull the plow the other direction.
Offered by Ron.
This is an inventive use of commonly available items. I see a slight problem with the
design - in that once one encounters the path of the cable, a person would need to duck
down and possibly let go of the wood bar that is being pushed around for a short space
of the turn. After a while in the low light conditions, this cable might get to be tiresome
and hard to see. With each person letting go of the bar at one point along the turn, this
loads the bearing the spool rides on which adds more friction, and also tends to loosen
the post in the ground due to side thrusts.
You may want to consider some alternatives. If one puts the spool at ground level, then one would need to step over the wire on each turn as one pushes it around. So this is still not optimum. One could build a platform about 3 ft. high to walk on so that the people pushing are above the wire. Another possibility is to have the wire go through a pipe that one steps over. Another possibility is to have the spool above one's head and the push bars on the bottom side of the spool. In this case, one has to carefully consider the forces involved on the center pole in the wet ground. The base would need to be strongly braced in this case. Still might need to duck down but at least you wouldn't need to let go of the push bar and cause extra load to the others pushing.
Offered by Mike.