Preferred stock may be sold to any person, member, or non-member, and may be redeemable or retireable by the association, on such terms and conditions as may be provided for by the articles of incorporation, and printed on the stock certificates. The by-laws, except as otherwise provided for in this Act, shall prohibit the transfer of the common stock of the association to persons not engaged in the production of agricultural products and such restrictions shall be printed upon every certificate of stock subject thereto.