In carrying out the purposes of the Act of June 22, 1936 (49 Stat. 1570), as amended and supplemented, the Secretary of the Army and the Secretary of Agriculture are authorized to cooperate with institutions, organizations, and individuals, and to utilize the services of Federal, State, and other public agencies, and to pay by check to the cooperating public agency, either in advance or upon the furnishing or performance of said services, all or part of the estimated or actual cost thereof; and to make expenditures for personal services and rent in the District of Columbia and elsewhere, for purchase of reference and law books and periodicals, for printing and binding, for the purchase, exchange, operation, and maintenance of motor-propelled passenger-carrying vehicles and motorboats for official use, and for other necessary expenses. The provisions of this section shall be applicable to any funds heretofore appropriated for the prosecution by the Secretary of Agriculture of works of improvement for measures of run-off and water-flow retardation and soil-erosion prevention upon watersheds.