This marketing order for alfalfa seed shall become effective after having been approved in a referendum of affected producers, by at least 51% of the affected producers of alfalfa seed having at least 65% of the volume of alfalfa seed produced, or by at least 65% of the affected producers of alfalfa seed having at least 51% of the volume of alfalfa seed produced, and after having been filed with the code reviser for not less than thirty days.