Any referendum conducted under the provisions of this Article may be held either on an area or statewide basis, as may be determined by the certified agency before such referendum is called; and such referendum, either on an area or statewide basis, may be participated in by all farmers engaged in the production of such agricultural commodity on a commercial basis, including owners of farms on which such commodity is produced, tenants and sharecroppers. In such referendum, such individuals so eligible for participation shall vote upon the question of whether or not there shall be levied an annual assessment for a period of three years in the amount set forth in the call for such referendum on the agricultural product covered by such referendum. Provided, that notwithstanding any other provision of this Chapter, the North Carolina Cotton Promotion Association, Inc., in 1967 shall hold a referendum, pursuant to law, for the years 1969 and 1970, or for the years 1969 through 1973, in its discretion. Thereafter, the North Carolina Cotton Promotion Association, Inc. shall conduct either triennial or sexennial referendums as provided by law. (1947, c. 1018, s. 10; 1967, cc. 213, 561.)