Agricultural reserves, preserved land and open space. On any parcel subject to any commitment limiting further development by reason of a sale of development rights, imposition of a conservation or similar easement, preserved as open space or participating in any similar program or used for agriculture, any site plan approval for the construction of agricultural buildings, structures and improvements shall require a maximum preservation of open space, the least possible disturbance of the prime agricultural soil, and maximum maintenance of unencumbered public vistas that still allow for efficient farming practice and, in all events, shall limit any such construction to buildings, structures and improvements that are of a true agricultural nature, are used solely for agricultural purposes, and are necessarily accessory to the principal agricultural use.