Local governments and counties shall be prohibited from enacting or enforcing ordinances or regulations within an agricultural preserve which would, as adopted or applied, unreasonably restrict or regulate normal farm structures or farm practices in contravention of the purpose of sections 473H.02 to 473H.17 unless the restriction or regulation bears a direct relationship to an immediate and substantial threat to the public health and safety. This section shall apply to the operation of farm vehicles and machinery in the planting, maintenance and harvesting of crops and in the care and feeding of farm animals, the type of farming, and the design of farm structures, exclusive of residences.