We had this problem when buying our place. I am pretty certain that because, although I already had 8 acres nearby, because the farm only had 12 acres, the acreage did not cause a problem with a residential mortgage because it was not enough land for a commercial enterprise, or words to that effect. But the mortgage is a residential one, and therefore I am not supposed to use the land for commercial gain, or would have to have a business mortgage, which would be higher payments I suspect.