Section 5. No lands shall be sold for less than three dollars per acre, and no lands which are or shall be susceptible of irrigation under any projects now or hereafter completed or adopted by the United States under legislation for the reclamation of lands, or under any other project for the reclamation of lands, shall be sold at less than twenty-five dollars per acre; Provided, that the state, at the request of the secretary of the interior, shall from time to time relinquish such of its lands to the United States as at any time are needed for irrigation works in connection with any such government project, and other lands in lieu thereof shall be selected from lands of the character named and in the manner prescribed in section twenty-four of the said Enabling Act.