When the land on which the building or improvement is situated is not in a city or town and exceeds in area one acre, any person having a lien, or his personal representative, may at any time prior to his filing his statement in the office of the judge of probate, select one acre in addition to the land upon which the building or improvement is situated which shall also be subject to the lien; such selection to include the land surrounding the said building or improvement, and contiguous thereto, and with the land on which the building or improvement is situated to constitute but one lot or parcel. When the land on which the building or improvement is situated is in a city or town and the improvement consists of two or more buildings united together, situated on the same lot or contiguous or adjacent lots, or of separate buildings upon contiguous or adjacent lots, or where the machinery, material, fixture, engine, boiler, work, or labor has been furnished for improvements or structures which are located on separate tracts or parcels of land but operated as an entire plant or concern, and erected under one general contract, the lien for the labor, materials, fixtures, engines, boiler, or machinery, so furnished, shall attach to all such construction or improvements, together with land upon which they are situated, and it shall not be necessary to file a separate lien for each lot, building, or improvement, but the party claiming the lien may elect to file a separate lien for each lot, building, or improvement.