Amounts received as loans from the Commodity Credit Corporation shall, at the election of the taxpayer, be considered as income and shall be included in gross income for the taxable year in which received.

If a taxpayer exercises the election provided for in subsection (a) for any taxable year, then the method of computing income so adopted shall be adhered to with respect to all subsequent taxable years unless with the approval of the Secretary a change to a different method is authorized.