The EPA considers scrap tires to be a hazardous material. The primary hazard is that they collect water and provide incubators for mosquito "wigglers".
There are regulations. They must be stored inside or wrapped in plastic. Alternatively, they must be sprayed with insecticides or mosquito larvicides at regular intervals. It is a felony for an unlicensed scrap tire holding yard (a farmer) to "store" more than four scrap tires outside. Penalties are a $400 fine or 100 days of community service.
Hauling more than ten scrap tires at a time requires licensing. Failure to have a license is a felony.
I don't know how farmers can use them as weights to hold down the covers on bunker silos. The EPA regulations are almost unreadable. I doubt that there is a single EPA employee who is intimately familiar with all of their regulations. There may be a caveat that the sidewalls be drilled so water can drain. I doubt that farmers orient the tires so the drain holes are at the very bottom.
Incidentally, I had communication with Marcus Brown. He read the comment about using tires to contain soil for the trees he is planting. He briefly considered it but rejected the idea. His primary reason for rejecting them was aesthetic. His operation will be open to public view and aesthetics matter. Many of us would stop eating sausage if we watched it being made.
I think not using tires is a good idea because somebody could get pissed at Marcus and sic the EPA on him. Not having scrap tires around the place gives them one less thing to bark about. Finally, arsonists LOVE scrap tires. Why give those who wish to destroy the tools of their trade?