Is the farm that the father promised to register to his son, and then died before completing that, part of the inheritance or does it belong to the son?

The farm is considered part of the inheritance and must be divided according to Islamic law among the heirs. It does not become your property merely because your father said he would register it in your name. A gift (hiba) is not complete except by possession, and justice between children must be observed in it. A bequest (wasiyya) to an heir is forbidden by Islamic law and is not effective unless all adult, sane heirs approve it.