The county board, in its sole discretion, may provide for the payment of the assessments in five equal annual installments, the unpaid balances of which shall bear interest at not to exceed the legal rate of interest or the interest which is borne by the warrants issued in payments of said project. In the event that the board elects to defer payments as provided in this section, warrants shall be given in payment of the costs of said project, which warrants shall be payable from collection of such assessments.