The board of supervisors of any county holding in trust the property of any agricultural society organized under any law of this state for the purpose of the holding and maintaining of agricultural, industrial and mechanical fairs, is hereby authorized and empowered in conjunction with said society to execute and deliver a mortgage on all or any of the real property of said society for the purpose of securing the payment of the obligations of such society contracted for or arising from the maintenance of such fair. The terms and conditions of such mortgage shall be subject to the discretion of such board of supervisors.