Check out rotational grazing on pasture with chicken tractors, Joel Salatin style. Lots of folks doing that with good success for hundreds to thousands of birds - layers or meat birds. The key is moving them often and giving the grass a chance to recover.
The problem with crop land is that the birds will tear things up. You’re also somewhat constrained by what’s ripe when.
That being said, a pasture system with supplemental food from the crop land (and then letting the flock in for fall cleanup) might work really well. Winter storage crops like pumpkin and squash would help with any winter feeding.