If you need the N from the Dap is there any reason to not use it for your P source? How does the N from dap compare to that from urea as far as being able to lay on the ground a few days before covering? I have some areas in fields that I need to go back and put a additional 46 units of P on . That 18 units on N in the dap is low cost N and I don't think that much more N on corn will hurt anything.