1. The agricultural land tax credit allowed each year shall be computed as follows: On or before April 1, the county auditor shall list by school districts all tracts of agricultural lands which are entitled to credit, together with the taxable value for the previous year, together with the budget from each school district for the previous year, and the tax rate determined for the general fund of the district in the manner prescribed in section 444.3 for the previous year, and if such tax rate is in excess of five dollars and forty cents per thousand dollars of assessed value, the auditor shall multiply the tax levy which is in excess of five dollars and forty cents per thousand dollars of assessed value by the total taxable value of the agricultural lands entitled to credit in the district, and on or before April 1, certify the amount to the department of revenue.
 2. In the event the county auditor denies a credit upon any such lands, the auditor shall immediately mail to the owner at the owner’s last known address notice of the decision thereon. The owner may, within thirty days thereafter, appeal to the board of supervisors of the county wherein the land involved is situated by serving notice of said appeal upon the chairperson of said board. The board shall hear such appeal promptly and shall determine anew all questions involved in said appeal and shall within ten days after such hearing, mail to the owner at the owner’s last known address, notice of its decision. In the event of disallowance the owner may, within ten days from the date such notice is mailed, appeal such disallowance by the board of supervisors to the district court of that county by serving written notice of appeal on the county auditor. The appeal shall be tried de novo and may be heard in term time or vacation. The decision of the district court thereon shall be final.