If a national marketing quota for wheat has been proclaimed for any marketing year, the Secretary shall determine and proclaim the amount of the national marketing quota for such marketing year not earlier than January 1 or later than April 15 of the calendar year preceding the year in which such marketing year begins. The amount of the national marketing quota for wheat for any marketing year shall be an amount of wheat which the Secretary estimates (i) will be utilized during such marketing year for human consumption in the United States as food, food products, and beverages, composed wholly or partly of wheat, (ii) will be utilized during such marketing year in the United States for seed, (iii) will be exported either in the form of wheat or products thereof, and (iv) will be utilized during such marketing year in the United States as livestock (including poultry) feed, excluding the estimated quantity of wheat which will be utilized for such purpose as a result of the substitution of wheat for feed grains under section
1339c of this title; less (A) an amount of wheat equal to the estimated imports of wheat into the United States during such marketing year and, (B) if the stocks of wheat owned by the Commodity Credit Corporation are determined by the Secretary to be excessive, an amount of wheat determined by the Secretary to be a desirable reduction in such marketing year in such stocks to achieve the policy of the chapter: Provided, That if the Secretary determines that the total stocks of wheat in the Nation are insufficient to assure an adequate carryover for the next succeeding marketing year, the national marketing quota otherwise determined shall be increased by the amount the Secretary determines to be necessary to assure an adequate carryover: And provided further, That the national marketing quota for wheat for any marketing year shall be not less than one billion bushels.