The Secretary shall make all loans under this subchapter upon the full personal liability of the borrower and upon such security as the Secretary may prescribe. The interest rates on such loans, except for guaranteed loans and loans as provided in paragraphs (2) and (3),^[1] shall be as determined by the Secretary, but not in excess of the current average market yield on outstanding marketable obligations of the United States with remaining periods to maturity comparable to the average maturities of such loans, plus an additional charge not to exceed 1 per centum as determined by the Secretary, which charge shall be deposited in the Rural Development Insurance Fund or the Agricultural Credit Insurance Fund, as appropriate, and adjusted to the nearest one-eighth of 1 per centum. The interest rate on any guaranteed loan made under this subchapter shall be such rate as may be agreed upon by the borrower and lender, but not in excess of a rate as may be determined by the Secretary.