Nor should he assess the kharaj up to the utmost that the land can bear; rather, he should leave the landowners something with which to meet extraordinary burdens and calamities.
In determining the kharaj, the assessor should choose the most suitable of three methods. The first is to assess it according to the measured acreage of the land. The second is to assess it according to the measured acreage of the crops. The third is to impose it as a proportional levy.
If it is assessed according to the acreage of the land, it is reckoned by the lunar year. If it is assessed according to the acreage of the crops, it has been said that it is reckoned by the solar year. If it is imposed as a proportional levy, it is reckoned when the crop has fully matured and been cleaned.
Once an amount has been established under one of these methods, together with the conditions applicable to it, that amount becomes fixed permanently. It may not be increased or reduced so long as the lands remain in their existing condition with respect to their irrigation arrangements and productive facilities. If their irrigation arrangements and productive facilities change, whether for the better or worse, there are two possibilities.
The first is that the improvement or deterioration occurs as a result of something done by the landowners themselves—for example, an increase resulting from the digging of canals or the development of water sources, or a decrease resulting from negligence in cultivation or abandoning a beneficial improvement. In that case, the kharaj remains as it was: it is not increased because of their improved cultivation, nor reduced because of its decline. Nevertheless, they are required to cultivate the land, for their own benefit and that of the recipients of the fayʾ, so that its deterioration does not continue and its revenue become unavailable.
The second possibility is that the change occurs through no fault of theirs, so that the decrease results from a canal bursting or a river becoming unusable. If repairing and restoring it is possible, the imam must undertake the work from the treasury, using the allocation designated for public interests; and the kharaj is waived for them until the work is completed. If restoring it is not possible, the kharaj on that land is waived for its owners when it can no longer be put to any use. If it can still be used for purposes other than cultivation, such as hunting grounds or pasture, it is permissible to impose a new kharaj according to what the hunting and grazing can bear. Such land is not treated like unclaimed wasteland (mawāt), upon whose hunting grounds and pastures no kharaj may be imposed, because this land is privately owned, whereas wasteland is open and unowned.
Khuḍr ibn Isḥāq related that a hunter asked Aḥmad about hunting in a thicket—that is, Qatr Bal—and said, “They prevent us from hunting there unless we give them something.” He replied, “Try your utmost not to give them anything; but if you make an agreement with them, do not betray them.”