Can property be claimed if used for agricultural purpose for my years

Hi, I am from andhra pradesh, but working in bangalore, my grand father is the only child to his father, recently my grand father got some documents from an old locker in house which consists of 10 acres land documents on my grand father's father name. We went and enquired that in registar office that land is still in my grand father's father name only but it was occupied by some one else and they are farming in that land for so many years. Now my question is do my grand father have rights to get that land back ? If yes, could you please tell us the procedure?