Planting in cornfields should be fine.
Corn produces roots that sprawl out only within the first 4"-6" of soil depth.
Marijuana is a taproot plant, and shallower soil depth roots are negligable. (I speak of in ground, in pots it's a whole different story)
where I'm at, the soil cracks and splits about a foot deep, on average. Never had any issues from the roots getting torn/snapped/ripped.
So as long as you feed heavy, you shouldn't have too many issues.