Within thirty days after the petition has been filed with the board of soil and water district supervisors, they shall fix a date, hour and place for a hearing thereon and direct the secretary to cause notice to be given to the owners of each tract of land, or lot, within the proposed subdistrict, as shown by the county records, and to each lienholder or encumbrancer of any such lands as shown by the county records and to all other persons whom it may concern, and without naming individuals all actual occupants of land in the proposed subdistrict, of the pendency and prayer of the petition and that all objections to establishment of said subdistrict for any reason must be made in writing and filed with the secretary of the soil and water conservation district at or before the time set for hearing.