Natural grasses are ok hunting wise and are better for the ducks nutritionally. If you want an impoundment that is not quite as good hunting but with good habitat, then go moist soil/natural. If you want a spot to kill more ducks and still have decnt habitat stick with corn. Weedy corn is the best of both worlds as they love corn as well as it it provides natural seeds as well as detritus for invertebrates, which are important in the late winter/ early spring. Just remember these ducks can go to the refuges and many many other places and find the natural foods. You want something they want, which in my experience is corn. We tried smartweed, jap millet, buckwheat etc and when we have all corn, it does better. I have a small place in va that is 1 acre corn and 1.5 acre natural (can only plant one acre so thats all we do or else it would be all corn). Once the corn is eaten out, most birds leave, no matter how much natural is in there. You can still kill a few but its not as good as the corn. just my .02
As to how to plant the corn, we plant it all and pick some to open it up. Creates open water and allows some waste grain to be utilized. We usually dont pick any more than 1/4 of our field.
"If you have to be crazy to be a duck hunter, i dont wish to be sane" Robert Ruark
Its always duck season, there is just a long break from february to september.