Any corporation organized and existing under and by virtue of the laws of the State of Nebraska if created not for private gain or profit and under legal restrictions which preclude it from being organized for private gain or profit, and if organized and existing for the purpose of promoting and advancing the interests of agriculture and farm husbandry in the State of Nebraska, having outstanding any bonds or debentures matured or about to mature, may refund such bond indebtedness or debentures in an amount not exceeding the existing unpaid principal and interest due on such bonds or debentures, by issuing new bonds or new debentures in exchange for bonds or debentures maturing or about to mature, or to be sold for the purpose of securing funds to redeem principal and interest of the bonds or debentures maturing or about to mature. Such new bonds or debentures shall not be issued in excess of the amount required to refund the existing indebtedness, shall not be sold or exchanged at less than par and shall not draw interest at a rate in excess of three percent per annum, which interest may be made payable annually or semiannually. No authority is hereby granted nor shall this section be construed to grant authority to any such corporation to increase its indebtedness, the sole object and purpose of this section being to authorize refunding of existing indebtedness.