Interestingly, accidentally making the soil too salty to support agriculture is one of the consequences of improperly managed irrigation over longish time scale

Interestingly, accidentally making the soil too salty to support agriculture is one of the consequences of improperly managed irrigation over longish time scales, like decades to centuries. It's well understood now but I don't believe that it was to ancient peoples. I don't know how this could be weaponized or if anyone ever made a serious attempt at it. But it's experienced as massive regional catastrophe when it does, and the cause is clear even if not understood. There are places in arizona and california where salt crystals visibly form on the surface of what used to be farmland: it's plausible this would have been seen in the irrigation agriculture societies of mesopotamia and the ancient eastern mediterranean. Certainly easy to make the jump to fantasizing/praying about it happening to your enemies, once you've seen or heard of it.