Could you post a google earth view so we can really help you? Just hide the coordinates(lat./long.) before you do.
If not, I'd say to put a trailcam on the edges of heavy cover, for example, where the hardwoods meet the crp/crops. Or near food sources with thick cover nearby.
Try glassing the fields(from a distance with binoculars) before sundown and you should be able to see where they're coming from. Good luck