Please note. If you have a SUBDIVIDED parcel, legally done so, then there is not a single 40 acre parcel. There are 2 parcels. Appraise only an identifiable parcel and you are totally complying with Fannie mae. The fact the owner has adjacent property is not an issue, even if the adjacent parcel by its nature affects the value. So if you have 80 acres and legally subdivide it into 5 acres and 75 acres. The 75 being a poultry farm and the 5 acres being a dwelling, then appraise the 5 acre tract as a perfectly legal 5 acre parcel. The fact the chicken farm may affect the value only means you address that issue. You have no obligation to address even the ownership of the other parcel unless the two parcels are sharing a well or driveway.