Agricultural uses, which shall include any use of land for crops, no use at all — such as land in soil bank, orchards, trees or forest lands and any other use pertinent to farming, agricultural research or any activity normally connected with farming. Such uses shall allow all types of structures normally associated with these uses, including dwelling units, storage bins, barns, sheds, toolhouses, garages, and any other use or facility ancillary to farming or open land. More than one (1) dwelling unit may be on agricultural land or a farm. Only by special permit of the Board of Adjustment may more than two (2) dwelling units be upon a single farm. The Board shall issue this permit after a hearing, based upon the compatibility of the proposed dwelling unit with the surrounding area. No trailers, trailer houses or mobile homes will be permitted to be occupied as a dwelling unit in the A-1 District.