Iowa Code § 458A.18: Mineral rights taxed separately.

All rights and interests in or to oil, gas, or other minerals underlying land, whether created by or arising under deed, lease, reservation of rights, or otherwise, which rights or interests are owned by any person other than the owner of the land, shall be assessed and taxed separately to the owner of such rights or interests in the same manner as other real estate. The taxes on such rights or interests that are not owned by the owner of the land shall not be a lien on the land.