The notice of hearing on the formation of a subdistrict shall be by publication once each week for two consecutive weeks in some newspaper of general circulation published in the county, the last publication of which shall be not less than ten days prior to the day set for the hearing on the petition. Proof of service shall be made by affidavit of the publisher, and be on file with the secretary of the soil and water district at the time the hearing begins. Notice of the referendum shall be made in the same manner.