There is hereby authorized to be appropriated for each fiscal year, beginning with the fiscal year ending June 30, 1957, the sum of $500,000,000 to enable the Secretary of Agriculture to further carry out the provisions of section 612c of this title, subject to all provisions of law relating to the expenditure of funds appropriated by such section, except that up to 50 per centum of such $500,000,000 may be devoted during any fiscal year to any one agricultural commodity or the products thereof.