(a) After his approval of any application for an exchange as provided in this subchapter, the Secretary may cancel and release, in whole or in part, any and all charges or liens against the entryman or against the relinquished farm unit which are within his administrative jurisdiction. In administering the provisions of this subsection the Secretary shall take into consideration other charges and liens and the rights and interests of other lien holders as to him may seem just and equitable.

(b) An entryman making an exchange under the provisions of this subchapter may be given credit by the Secretary upon any land development charges made by the United States in connection with the lieu farm unit for any such charges paid to the United States in connection with the original unit. A resident owner making an exchange under the provisions of this subchapter may, to the extent, to which he or, in the case of a widow, widower, heir, or devisee, his spouse or ancestor, as the case may be, has paid to the United States the purchase price of the original farm unit, be given credit by the Secretary upon the purchase price of his lieu farm unit; such credit may also be applied in the manner and circumstances provided in section 451b of this title upon irrigation construction charges for or properly assignable to his lieu farm unit.