Whenever during any calendar year the Secretary determines that the total supply of cotton for the marketing year beginning in such calendar year will exceed the normal supply for such marketing year, the Secretary shall proclaim such fact and a national marketing quota shall be in effect for the crop of cotton produced in the next calendar year. The Secretary shall also determine and specify in such proclamation the amount of the national marketing quota in terms of the number of bales of cotton (standard bales of five hundred pounds gross weight) adequate, together with (1) the estimated carry-over at the beginning of the marketing year which begins in the next calendar year and (2) the estimated imports during such marketing year, to make available a normal supply of cotton: Provided, That beginning with the 1961 crop, the national marketing quota shall be not less than a number of bales equal to the estimated domestic consumption and estimated exports (less estimated imports) for the marketing year for which the quota is proclaimed, except that the Secretary shall make such adjustment in the amount of such quota as he determines necessary after taking into consideration the estimated stocks of cotton in the United States (including the qualities of such stocks) and stocks in foreign countries which would be available for the marketing year for which the quota is being proclaimed if no adjustment of such quota is made hereunder, to assure the maintenance of adequate but not excessive stocks in the United States to provide a continuous and stable supply of the different qualities of cotton needed in the United States and in foreign cotton consuming countries, and for purposes of national security; but the Secretary, in making such adjustments, may not reduce the national marketing quota for any year below (i) one million bales less than the estimated domestic consumption and estimated exports for the marketing year for which such quota is being proclaimed, or (ii) ten million bales, whichever is larger. Such proclamation shall be made not later than October 15 of the calendar year in which such determination is made. Notwithstanding the foregoing provisions of this section, the national marketing quota for cotton for 1957 and 1958 shall be not less than the number of bales required to provide a national acreage allotment for 1957 and 1958 equal to the national acreage allotment for 1956: Provided, That if the acreage allotment for any State for 1957 or 1958 is less than its allotment for the preceding year by more than 1 per centum, such State allotment shall be increased so that the reduction shall not exceed 1 per centum per annum, and the acreage required for such increase shall be in addition to the national acreage allotment for such year. Additional acreage apportioned to a State for 1957 or 1958 under the foregoing proviso shall not be taken into account in establishing future State allotments. Notwithstanding any other provision of this chapter, the national marketing quota for upland cotton for 1959 and subsequent years shall be not less than the number of bales required to provide a national acreage allotment for each such year of sixteen million acres.