Neb. Rev. Stat. § 10-507: Neb. Rev. Stat. § 10-507

The county board of any county issuing bonds under sections 10-501 to 10-509 shall levy a tax annually for the payment of the interest on the bonds. An additional amount shall be levied and collected sufficient to pay the principal of such bonds at maturity. Not more than twenty percent of the principal of such bonds shall be levied and collected in any one year.