First off: 200K?! That's a really large city, an exceptionally large one I think for most AD&D style milieus, like there'd only be a few of that size or larger, typically
Jürgen Hubert said
Make some Soylent Green.
___________
Now, see this is along the lines of what I'm about to suggest, vis a vis Purify Food And Water. There are numerous instances where people besieged had to consider Second Harvest options (I think there's something in the Old Testament to that effect where the attacking army said come on out now or you'll have to consume your own urine/excrement)--but seriously, though, if clerics have the power to Purify food matter, why wouldn't Second Harvest options be on the table at least for consideration? It seems like the spell could just hasten the process of putting fertilizer into the soil, composting it, nourishing the plants, eaten by the animals, and back into human consumption--seems like something a Druid would especially highly recommend as really its only a part of the Natural Cycle, simply magically or divinely accelerated.