KSA 8-142 and 8-143 describes what a farm tag can be used to legally haul. Any activities outside of the statute would be in violation of the farm tag.
8-142. Unlawful acts. It shall be unlawful for any person to commit any of the following acts and except as otherwise provided, violation is subject to penalties provided in K.S.A. 8-149, and amendments thereto:
Ninth: To operate on the highways of this state a farm truck or farm trailer other than to transport: (a) Agricultural products produced by such owner; (b) commodities purchased by the owner for use on the farm owned or rented by the owner of such vehicles; (c) commodities for religious or educational institutions being transported by the owner of such vehicles for charity and without compensation of any kind, except as provided in K.S.A. 66-1,109(c), and amendments thereto; or (d) sand, gravel, slag stone, limestone, crushed stone, cinders, black top, dirt or fill material to a township road maintenance or construction site of the township in which the owner of such truck resides.
Tenth: To operate a farm truck or truck tractor used in combination with a trailer or semitrailer for a gross weight which does not include the empty weight of the truck or truck tractor or of the combination of any truck or truck tractor and any type of trailer or semitrailer, plus the maximum weight of cargo which will be transported on or with the same; and such farm truck or farm truck tractor used to transport a gross weight of more than 54,000 pounds shall have durably lettered on the side of the motor vehicle the words "farm vehicle—not for hire."
Thirteenth: To operate on the highways of this state a farm trailer carrying more than 6,000 pounds without being registered and the registration fees paid thereon.