mossberg93,

incorporating the manure, means tilling or mixing it in the soil, keyshunter, is right about loosing nitrogen to the atmosphere, manure is not as bad as chemical nitrogen though. incorporating saves the nitrogen from being lost.
If you apply it right before a good rain, it is not as much lost even with out tilling. Also if you have a limited amount of manure, a good way to make it go farther, is to apply it when the corn is about 10 to 14 inches tall.

Not trying to be a know it all... Just like helping people