The council of any city or town to which territory has been added may, by ordinance, allow a lower rate of taxation to be imposed for a period not to exceed ten years after the effective date of the annexation upon the real estate or any portion thus added to its corporate limits, than is imposed on similar property within its limits at the time such territory was added. Such differences in the rate of taxation hereafter shall be established annually and shall bear a reasonable relationship to differences between nonrevenue-producing governmental services giving land urban character which are furnished in the area added as compared to other areas in the city or town.