An act to repeal and re-enact, with amendments, Section 19(b) of Article 81 of the Annotated Code of Maryland (1969 Replacement Volume), title "Revenue and taxes," subtitle "Method of assesment," excepting certain lands from assesment under Section 19(b)(1) of said article, title and subtitle; and amending the law relating to the calculation and payment of the deferred tax on certain land used for agricultural purposes