(2) Contract provisions for repayment of any loan from the United States, and the bonds securing the payment of the same, if any are issued, may be of such denomination, for such term not exceeding 50 years and may call for the payment of such interest not exceeding seven percent per annum, may provide for such installments and for repayment of the principal at such times, as may be required by the federal laws and as may be agreed upon between the district board and the United States agency. [1969 c.668 §26c; 1973 c.86 §1]