“Any person who, prior to June 16, 1955, made a valid desert-land entry on lands subject to such Act of June 22, 1910 [sections 83 to 85 of this title], or of July 17, 1914 [sections 121 to 123 of this title], may, if otherwise qualified, make one additional entry, as a personal privilege, not assignable, upon one or more tracts of desert land subject to the provisions of such Acts, as hereby amended, and section 7 of the Act entitled ‘An Act to stop injury to the public grazing lands by preventing overgrazing and soil deterioration, to provide for their orderly use, improvement, and development to stabilize the livestock industry dependent upon the public range, and for other purposes’, approved June 28, 1934, as amended (48 Stat. 1269, 1272; 43 U.S.C. 315f). The additional land entered by any person pursuant to this section shall not, together with his original entry, exceed three hundred and twenty acres, and all the tracts included within the additional entry authorized by this section shall be sufficiently close to each other to be managed satisfactorily as an economic unit, as determined under rules and regulations issued by the Secretary of the Interior. Additional entries authorized by this section shall be subject to all the requirements of the desert-land law.”