It shall be lawful for any citizen of the United States, or any person of requisite age ''who may be entitled to become a citizen, and who has filed his declaration to become such'' and upon payment of 25 cents per acre - to file a declaration under oath with the officer designated by the Secretary of the Interior of the land district in which any desert land is situated, that he intends to reclaim a tract of desert land not exceeding one-half section, by conducting water upon the same, within the period of three years thereafter: Provided, however, That the right to the use of water by the person so conducting the same, on or to any tract of desert land of three hundred and twenty acres shall depend upon bona fide prior appropriation; and such right shall not exceed the amount of water actually appropriated, and necessarily used for the purpose of irrigation and reclamation; and all surplus water over and above such actual appropriation and use, together with the water of all lakes, rivers, and other sources of water supply upon the public lands and not navigable, shall remain and be held free for the appropriation and use of the public for irrigation, mining, and manufacturing purposes subject to existing rights. Said declaration shall describe particularly said one-half section of land if surveyed, and, if unsurveyed, shall describe the same as nearly as possible without a survey. At any time within the period of three years after filing said declaration, upon making satisfactory proof to the officer designated by the Secretary of the Interior of the reclamation of said tract of land in the manner aforesaid, and upon the payment to such officer of the additional sum of $1 per acre for a tract of land not exceeding three hundred and twenty acres to any one person, a patent for the same shall be issued to him. Except as provided in section 3 of the Act of June 16, 1955, as amended, no person may make more than one entry under sections 321 to 323, 325, and 327 to 329 of this title. However, in that entry one or more tracts may be included, and the tracts so entered need not be contiguous. The aggregate acreage of desert land which may be entered by any one person under this section shall not exceed three hundred and twenty acres, and all the tracts entered by one person 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