39. ¹[* * *] when an improvement levy has been imposed in respect of any agricultural land- (a) the rent payable for such land at the time of the imposition of the levy or fixed thereafter in accordance with the provisions of clause (b) shall not be enhanced on account of- (i) benefits derived from the construction of any improvement work, or (ii) an increase in the productive powers of the land due to fluvial action; (b) if a settlement is made of such land with a tenant thereafter, the rate of rent at which such land is settled shall not exceed the average rate of money rent payable, at the time of such settlement, by tenants of a similar class for land of a similar description and with similar advantages in the vicinity, and any rent in excess of such rate shall not be recoverable: ²[* * *] A stipulation in any contract by which a tenant taking settlement of such land agrees to pay any amount in excess of such rent, otherwise than as salami, shall not be binding on such tenant to the extent of such excess.