Whenever such action is deemed to be in the public interest, the Secretary of Agriculture is authorized to pay from any appropriation available for the protection and management of the national forests all or any part of the cost of leasing, seeding, and protective fencing of public range land (other than national forest land) and privately owned land intermingled with or adjacent to national forest or other land administered by the Forest Service, if the use of the land to be seeded is controlled by the Forest Service under a lease or agreement which in the judgment of the Chief of the Forest Service gives the Forest Service control over the land for a sufficient period to justify such expenditures: Provided, That payment may not be made under authority of this section for the seeding of more than one thousand acres in any one private ownership: Provided further, That payment may not be made under authority of this section for the seeding of more than twenty-five thousand acres in any one fiscal year: Provided further, That the period of any lease under this authority may not exceed twenty years.