Neb. Rev. Stat. § 23-319: Neb. Rev. Stat. § 23-319

After sixty days from the completion and approval of the work it shall be the duty of the county board to issue the bonds of the county in the amount of the assessment remaining unpaid at said time, payable in not to exceed ten equal annual installments with interest on deferred payment at seven percent per annum, and said special assessment and taxes shall constitute a sinking fund for the payment of the bonds and interest.