1. Ducks will use the fields. Water doesn't need to be present, if you have left over crops. A good example is a harvested spud field. When the northerns show up, you will see them all over the spud fields, along with swans, Canadian's and snows in some locations.
2. There are birds you can't shoot. Read the regs, use common sense and don't blast it, unless you can ID it. If you can only ID birds that are shot, you need to spend more time in the field and do some studying of the various birds.