There is a lot more to it than does a duck like corn, etc.
What area are you in, what duck spp are around, and what is the weather like.
Mallards pile in to corn when everything is frozen, they are getting cold and need a high energy food. They'll stay in the wetlands as long as they can. If you just have OTM (other than mallards), stick with natural or something they can easily eat.
But first add water, that is what they really want with their meal.
But to what is the best to bait a duck...banding crews use bright yellow barley