My cows do it. when they poop. :lol2:
Most organics applied to the soil are going to add micro nutrients. There may be some commercial sources but I am not aware of any that would be cost feasible for a pasture.
Sludge would be your best bet, but as brought up on another thread make sure it has been tested for heavy metals. Chicken litter would help. I know some that use manure from the sale barn but I would be afraid of bringing in other disease with it.
You would be amazed at how well an abused pasture will come back after a little rest and going back with proper stocking rates and management practices.