The down side to AMS is that it's only 21-0-0 vs urea which is 42-0-0. So it takes twice as much, which is a bummer. I did read that it will last a little longer on the surface than urea if you broadcast without incorporating it like I do. Can't always time it right with rain.
Oh, and I mix the spray grade AMS with my water when I spray herbicide. Next year, I'll test again and maybe my sulfur will be up some.