The concern with either side dressing method, urea over the top or 28% over the top with a sprayer, is that you are totally dependent on nature providing a good rain shortly after you pull out of the field or you are going to lose a potentially significant portion of whichever product you apply by either method.

Either product should be applied beneath the soil surface and covered, in my opinion and experience or sooner or later you will pay for the experience. Over application rates tend to cover the effects of no rain but cost dearly.

I side dress 28% on 60" centers 4 or 5" deep with coulters and have had excellent results.

Jim at Dawn