In order to buy agriculture land in Karnataka, you need to full fill Section 79 (a) and Section 79(B) of land reform act. which states that the person who buys a agri land should be a farmer anywhere in India, and should not have total income of 25 lacks. (total income from the family).
when you buy the agri land, you can get it registered in the sub register office, where they will not ask you any question during registration. Problem arises only when the document goes from sub registrar to revenue inspector for further process and to issue RTC or Pani in your name,
some Revenue Inspectors will take bribe and say they will do it for you, but its illegal and you will be in trouble later.
so talk to a lawyer, before moving forward.