There is established a working capital fund of $300,000, to be available without fiscal year limitation, for expenses necessary for furnishing facilities and services by the Agricultural Research Center to Government agencies. Said fund shall be reimbursed from applicable appropriations or other funds to cover the charges for such facilities and services, including handling and related charges, for equipment rentals (including depreciation, maintenance, and repairs), for supplies, equipment and materials, stores of which may be maintained at the Center, and for building construction, alterations, and repairs, and applicable appropriations or other funds may also be charged their proportionate share of the necessary general expenses of the Center not covered by the annual appropriation.