I really have a hard time understanding urea, all the articles i have read talk like it is this real sensitive product, and if you look at it wrong it will disappear. When i spill some on the yard i scoop as much as possible with my hand brushing it into a shovel, i have a dead spot for years. I use it to kill weeds around my building's, i grab handfuls and pepper the ground and the dirt stays black. i tried it with a pail of S15 that sat for over a year in the shop it was laying on top of the ground and it did the opposite i had the biggest weeds ever seen.
My dad for some reason used to clean out the drill and put urea in old canola bags and leave them hidden all over in the back of buildings, some were close to 20 years old, and hard as a rock, but when i cut them open after they bleed for years and corroded everything near by, they still were as powerful as the fresh stuff. they way things are stated why didn't 20 lbs of urea evaporate when sitting in a weaved plastic bag for over 15 years. urea to me acts like creeping oil it melts with moisture and thins and bleeds along in the earth. As for the dead spots i know there is still a toxic amount of nitrogen there, and not just a high salt index, because at the edge where the grass grows it is the thickest, and greenest where the concentration drop's down not to burn plants, and if it was a salt index the plant's would be the weakest at the edge then getting normal the farther out you go from the spill. and it is exposed to all the elements of rain and snow to leach out and evaporate.
Another place that dad shoveled about hundred pounds of 46-0-0 out of the truck, and flung it on the field right on top of the earth where it stayed all year, and burnt the crop in those spots. to this day the crop still lodges in this area and this was an area on top of a clay hill that had such spindly crop it was almost not worth farming. that is going on 7 years now, and still you can see where every scoop landed and smeared. The way they talk about urea and its volatilization it should be gone in a year or two. the nitrogen in the soil on that hill will outlive my dad and he was done farming about 5 years ago.
i don't know, what i read is not reflecting what i see on my farm. maybe i am full of it. but i have banded with my hole drill, and broadcasted and incorporated with my cultivator, with the same amounts and i can't tell the difference. Maybe i just don't know what to look for, but my gut says it is not that critical as long as it is in the ground and covered.