To obtain revenue for extraordinary expenses incurred by reason of the national economic emergency, there shall be levied processing taxes as hereinafter provided. When the Secretary of Agriculture determines that any one or more payments authorized to be made under section 608 of this title are to be made with respect to any basic agricultural commodity, he shall proclaim such determination, and a processing tax shall be in effect with respect to such commodity from the beginning of the marketing year therefor next following the date of such proclamation; except that (1) in the case of sugar beets and sugarcane, the Secretary of Agriculture shall, on or before the thirtieth day after May 9, 1934, proclaim that rental or benefit payments with respect to said commodities are to be made, and the processing tax shall be in effect on and after the thirtieth day after May 9, 1934, and (2) in the case of rice, the Secretary of Agriculture shall, before April 1, 1935, proclaim that rental or benefit payments are to be made with respect thereto, and the processing tax shall be in effect on and after April 1, 1935. In the case of sugar beets and sugarcane, the calendar year shall be considered to be the marketing year and for the year 1934 the marketing year shall begin January 1, 1934. In the case of rice, the period from August 1 to July 31, both inclusive, shall be considered to be the marketing year. The processing tax shall be levied, assessed, and collected upon the first domestic processing of the commodity, whether of domestic production or imported, and shall be paid by the processor. The rate of tax shall conform to the requirements of subsection (b). Such rate shall be determined by the Secretary of Agriculture as of the date the tax first takes effect, and the rate so determined shall, at such intervals as the Secretary finds necessary to effectuate the declared policy, be adjusted by him to conform to such requirements. The processing tax shall terminate at the end of the marketing year current at the time the Secretary proclaims that all payments authorized under section 608 of this title which are in effect are to be discontinued with respect to such commodity. The marketing year for each commodity shall be ascertained and prescribed by regulations of the Secretary of Agriculture: Provided, That upon any article upon which a manufacturers’ sales tax is levied under the authority of the Revenue Act of 1932 and which manufacturers’ sales tax is computed on the basis of weight, such manufacturers’ sales tax shall be computed on the basis of the weight of said finished article less the weight of the processed cotton contained therein on which a processing tax has been paid.