Bonds issued by any irrigation district under the provisions of this chapter must be in the denominations and form, be subject to redemption with or without premium, and be subject to any other terms or conditions as the board of directors may determine, and must mature in not more than forty years from the date of the bonds. If the maturities are serial, the first installment of principal must fall due not more than three years, and the last installment not more than forty years, from the date of the bonds.