Each soil conservation district is administered by five (5) supervisors. Three (3) are elected in a district (county) wide election. Two (2) are appointed by the State Soil Conservation Committee. Each supervisor shall serve a three (3) year term and shall hold office until his successor has been elected or appointed and has qualified. Vacancies shall be filled for the unexpired term. The selection of successors to fill an unexpired term, or a full term, shall be made in the same manner in which the retiring supervisors shall, respectively, have been selected. The supervisors shall designate a chairman and may, from time to time, change such designation.