Watch them in the evening and see where they roost. I bet they are roosting very close to that field and may even fly down out into the field first thing in the morning if you put out a few decoys in a visible location close to where they are roosted. The objective is to get the toms to fly directly to your decoys before the hens fly down. Throw a jake decoy out there too just in case a hen flys down first to keep her there. Nothing beats a live decoy to help you. I've done this many times with success. Good luck.