Said referendum shall be upon the question of whether or not the farmers eligible for participation therein and voting therein shall favor an assessment upon themselves for the period of the next three tobacco marketing years, in an amount in each of said years as determined by or to be determined by the board of directors of Tobacco Associates, Incorporated but not more than four dollars ($4.00) per acre per year on all flue-cured tobacco acreage in the State of North Carolina, for the purpose of providing farmer participation in the fund and through the agency established for the stimulation, expansion and development of export markets for flue-cured tobacco and the encouragement of the use of flue-cured tobacco everywhere. (1959, c. 309, s. 8; 1987, c. 294, s. 6; 1989, c. 349, s. 3.)