If you aren't so very arid as to have the natural processes of decay stopped by the mummifying dryness and have enough land for the poop to be well-spread out it shouldn't be a significant problem.
I don't free range, but small amounts of poop in grass would vanish promptly just like the wild bird droppings and the deer droppings.
These probably help:
This is the world's bravest beetle, having gone into the run to get a dung ball and roll it out through the electric fence without...