Per RBI website, If you aquired the agriculture land when you were an Indian citizen You may continue to hold agriculture/farm land even after bocoming US citizen.
Please visit this website for more Q & A
http://www.rbi.org.in/index.dll/550...e=07/16/04&s1secid=0&s2secid=0&secid=20/0/0#8
Here is the information from RBI website. I hope this helps.
Q.46. Can NRI who had acquired immovable property viz., residential/commercial property/agricultural land/plantation property/farm house in India while he was a person resident in India continue to hold or transfer such immovable property? In which account the sale proceeds may be credited?
A.46. Yes, under the provisions of Section 6 (5) of the Foreign Exchange Management Act, 1999 NRI who had acquired immovable property in India while he was a person resident in India may continue to hold such property. Under the general permission available he may transfer by way of sale or gift agricultural land/plantation property/farm house in India to a person resident in India who is a citizen of India and may transfer by way of sale or gift residential/commercial property in India to a person resident in India or to a NRI/PIO. The sale proceeds may be credited to NRO account.
Q.47. Can a PIO who had acquired immovable property viz., residential/commercial property/agricultural land/plantation property/farm house in India while he was a person resident in India continue to hold or transfer such immovable property? In which account the sale proceeds may be credited?
A.47. Yes, under the provisions of Section 6 (5) of the Foreign Exchange Management Act, 1999, PIO who had acquired immovable property in India while he was a person resident in India may continue to hold such property. Under the general permission available he may transfer agricultural land/plantation property/farm house in India by way of sale or gift to a person resident in India who is a citizen of India and residential/commercial property in India by way of sale to a person resident in India and way of gift residential/commercial property in India to to a person resident in India or to a NRI/PIO. However, if a PIO is a citizen of Pakistan or Bangladesh or Sri Lanka or Afghanistan or China or Iran or Nepal or Bhutan he should seek prior approval of Reserve Bank for transfer of such immovable property in India. The sale proceeds may be credited to NRO account