I would first put effort into learning their habits and patterns. Where do they roost? What other paths do they take? Are there other fields that they frequent? If there is no access to them, and you are stuck trying to get them off that field to an available area (do they go there on their own ever?), use decoys (only high quality ones are worth a hoot, IMO), and calls. I'm not a huge believer in my local birds coming to a call or decoy. Out my way (by my opinion only) they find comfort an curiosity in decoys and limited calls, but not the need to rush out to them.
Best of luck! Post pics!