The use of land for agricultural purposes or the construction of buildings or structures incident to the use for agricultural purposes of the land on which such buildings or structures are located in any "S-1" or "AF" district and in any "M-1" or "M-2" district, provided the area of any single ownership used for agricultural purposes in an "M" district is at least ten acres, shall be permitted and no improvement location permit shall be required for any such agricultural building or structure.