An under-raiyat may, with the permission in writing of the raiyat, or if permission is refused without sufficient reason or is not given within two months, after obtaining the orders of the competent authority in the prescribed manner, make at his own expense any improvement to the land held by him, but shall not become liable to pay a higher rate of rent on account of any increase of production or of any change in the nature of the crop raised, as a consequence of such improvement.