Remember All That Land-Redeeming in the Book of Ruth?By Rabbi Jack Abramowitz
As mentioned, the land of Israel was divided among the families of the Tribes and could not be sold permanently, only leased until the next Jubilee. If financial straits force someone to sell a hereditary field, a relative of the seller can redeem it from the buyer, even against his will. (The seller can also do it himself if his financial picture improves.) They just have to calculate how much use the buyer got and how much time remains until the next Jubilee.
If nobody redeems it, it automatically reverts back to the original owner in the Jubilee year.