NEW DELHI: The Supreme Court on Tuesday said all state governments must implement one-nation, one ration card scheme by July 31.A bench headed by Justice Ashok Bhushan passed a slew of directions to the Centre and state governments for the benefit of the migrant workers. The top court directed all state governments to implement one-nation, one ration card scheme, which allows migrant workers to avail ration benefits from any part of the country, by July 31.