ORIGINAL: MeanV2
Urinating on the ground is just part of the scent puzzle at a scrape. Bucks work overhanging branches at all times of the year. I would say it's timing, mood of the buck, etc. I'm not even sure the ground is the most important part of a scrape. A lot of animals will urinate in a scrape, Coyote, Fox, Man[8D]etc.
Dan
Good point, bucks tend some scapes year round. They may not be aggressively pawing the ground and urinating in itbut they do a lot of scent marking through the glands around their eyes/foreheads(orbital glands) on overhanging branches. J. Ozaga wrote an article called Springtime Signposts which included research on year round buck scraping activity and it was very interesting. They actually made "ideal" scraping areas after the season and during the spring by manipulating branches near travel areas and had something like 60% activity once the season rolled around and these were completely man manipulated scrape areas. I can't find the link but if anyonecan it was a pretty cool read.
I'm doing some expeimenting of my own right now with the same theory.