As a rural resident and frequent observer of forage production techniques, it's my duty to inform you that, in my neck of the woods at least, they're called "Big Rounds". Not to be confused with "Big Squares", a similar size and weight, but rectilinear in shape. And "Small Squares", which are the traditional hay bales.
It's absolutely amazing how mechanized this process has become. A single worker can roll up dozens of acres of Big Rounds in a few hours, and in a few hours more, they're all gone. Packed off to feed animals throughout the winter.
I've been known to reclaim large used pieces of that white plastic for my own nefarious photographic uses. Tough, strong and white, it makes a great reflector and an even better light tent.
