Hang in there. I mainly hunt public land and do quite well. I think there are a few things to look at when choosing which land too hunt. First, try to be the first person in there for the day or even longer. Second, I always look for public land that has food on it or nearby. Specifically I look for corn or soybeans. Third, the less it gets hunted the better. And finally go to the back corner or that spot that looks the hardest to walk. It sounds like you’re out doing the work and have a good dog, so hang in there. The more the crops come out, the more birds will be looking for other places to hide. I’ve ridden in the combine with my cousins and its amazing to see the amount of birds in a cornfield. As others have said the farther away from the cities, the less the birds have been hunted. I live in Elk River and usually drive atleast an hour west before hunting unless my friend with a German shorthair named Star calls me.
If you want to drive to the Marshall or Willmar area, I can give you some spots to try. I’ve walked about all of them and keep a map and stats from years past.