The Secretary shall, not later than November 15, of the calendar years 1970 through 1976 proclaim a national cotton production goal for the 1971 and subsequent crops of upland cotton. The national cotton production goal for any year shall be the number of bales of upland cotton (standard bales of four hundred and eighty pounds net weight) equal to the estimated domestic consumption and estimated exports for the marketing year beginning in the calendar year for which such national cotton production goal is proclaimed, plus an allowance of not less than 5 per centum of such estimated consumption and estimated exports for market expansion except that the Secretary shall make such adjustments in the amount of such production goal as he determines necessary after taking into consideration the estimated stocks of upland cotton in the United States (including the qualities of such stocks) and stocks in foreign countries, which would be available for the marketing year, to assure the maintenance of adequate but not excessive carryover stocks in the United States (not less than 50 per centum of the average offtake for the three preceding marketing years) to provide a continuous and stable supply of the different qualities of upland cotton needed in the United States and in foreign cotton consuming countries and, in addition, to provide an adequate reserve for purposes of national security.