Elisha R. Smith, an Oak Bluffs farmer for more than three-quarters of a century and for more than two decades the president of the Martha’s Vineyard Agricultural Society, died last Friday at his home in Vineyard Haven at the age of 90. It was thanks to his determination, hard bargaining and skill at dealing with people that, in 1992, the society acquired the land that is the site of today’s Agricultural Hall. The acquisition of that West Tisbury Panhandle property where the annual fair is held was one of the proudest moments of his life, Elisha Smith said.