Thanks to Jan Slinsky for posting this YouTube video showing a center-pivot system used for tilling a small plot of land.
While requiring more energy than tillage-free management would, this system has the advantage of operating directly on electricity, meaning that there's no necessary dependency on petroleum to keep it running. It has two electric motors, which appear to be in the 2-3 horsepower range. Using both, its maximum power requirement should be no higher than 5 KW. Using just the motor that drives the wheel at the end of the rotating beam, which would be the more common case, the maximum power requirement should be no higher than 2.5 KW.
It also has the advantage of being usable now. In fact, to judge by the video, it appears to already have been in regular use for several seasons.