I really can not get these figures right.
I have 1 farm with millet; in tab 'Agriculture' / 'Food Supply' it says: supplies 2.9 loads/month. When the harvest is in the warehouse, I only get 15 loads.
I take a farm, half millet, half cabbage (so overlapping most of the time), the 'Food Supply' tab says I would get 1.5 loads of millet and 1.4 loads of cabbage. When both harvests are in, I did get 15 loads.
I take a farm, half wheat, half cabbage, the 'Food Supply' tab says the same as above, but when 12 months are gone (starting from planting the cabbage), I have 12 loads of cabbage and 10 loads of wheat (because no overlapping here).
However, if you take the figures from the 'Food Supply' tab and calculate how much food you need and how much you supply (provided you have only 1 type of housing), it matches.
So one might think that the output of a farm is not important, as long as it has water under it and the needed amount of workers. But a game that simulates an economy should not work that way; or if it does, it is not worth playing.
What am I missing here?
What *I* think you're missing, is that the workers on a farm actually work only 4 months per year on each crop (5 if you add the harvest month). If each farm has only one crop, all 15 loads are of that same type, which has been worked on for only 5 months. The other 7 months of the year, those workers could have been reallocated to other jobs. So those months should not be included in the calculation.
15 loads of crop divided by 5 active months, equals three loads per month.
The calculation *seems* to go wrong when you have multiple crops per farm: because the crops don't all grow in the same season, your farm is occupied longer, but still outputs the same total number of loads. So it's more effective to have a dedicated farm for each crop. However, at some point you'll find that reallocating those workers twice a year for each farm gets tedious. And on top of that, you'll have so many workers that you don't know what to do with, that leaving them on the farm continuously is much easier (as it prevents unemployment issues). Then it no longer matters if a farm serves only one, or all five crops. The total output won't change, after all.