Land reform acts apradesh

My grandfather was having a cultivatable land of 20 acres in 1950's, in Andhra Pradesh. Suddenly one day he said we lost all the land due to some law was introduced by the Govt of AP. The essence of that law is the actual cultivator (Rythu) will get right the land on whose name the cultivation is going on instead of the actual owner (My Grand Father). I am interested to know which is that act? When it was introduced? Otherwise from where can I find the details of that law?