I am writing a work of fiction and need to get a "reality test"
feel for how many people a square kilometer (etc) of land could
plausibly be expected to support.

If this is not the right NG, could someone suggest one, please?

Otherwise, here's an outline of the (NB) fictional situation:-

The land is former estuarial mud, like that produced by the UK's
River Thames. For story reasons too complex to detail here, the
land suddenly came under cultivation about thirty years ago using
essentially horse-aided manual techniques, by people with a sound
knowledge of modern agriculture but limited access to machinery
and artificial fertilisers. Mixed crops are raised, rotated and
all that. They have the kind of tools a good manual workshop or
smithy could make.

The climate is basically hot desert -- think of the US Mojave or
northern Sahara deserts: dry air, lots of strong sunshine, little
rain. Frost might occur but low temperatures are more likely to
be due to night-time cooling, as the altitude is about 100 ft.

Happily, good water is absolutely not a problem. Pests are few.

I imagine that by now the land is becoming used up, despite their
efforts to feed it with whatever, ahem, fertiliser comes to hand.

Would anyone care to guess at the productivity of 8.3 square Km?

TIA.
--
Andrew Stephenson