Neb. Rev. Stat. § 10-405: Neb. Rev. Stat. § 10-405

It shall be the duty of the proper officers of such county or city to cause to be annually levied, collected, and paid to the holders of such bonds a special tax on all taxable property within the county or city sufficient to pay the annual interest and principal of the bonds. Not more than twenty percent of the principal of such bonds shall be collected in any one year.