I know that I do not understand agricultural demand.
Suddenly, this city has high Ag demand. It did not use to.
Could cap relief of other development push up Ag demand?
Could regional population?
It is great that now I might grow some CAM Ag. But I have no idea why.
If I remember right, I-AG (I-R) was designed different from all other zones to be entry level industry helping to grow population on first stages and rarely becoming negativ in desire so even little children can play through the first three grow stages of a city tile without understanding the more complex mechanics.
Therefore I-AG demand mainly depends on tax rate and responds mainly to tax rate but different to education, because of having two parts giving jobs: the fields and the lots. While the fields give many jobs, the tax comes from the R$-lot and so will be always low compared to the amount of jobs. So soon I-AG isn't effective and you don't need it for further growth of the city tile.
Therefore, if I rembember, right, farm jobs work different from the know education/demand mechanic. This was already mentioned by RippleJet here (https://sc4devotion.com/forums/index.php?topic=963) and then investigated by Corihere (https://community.simtropolis.com/forums/topic/73840-the-505-year-education-experiment/). You have to scroll down half way in this thread until the discussion of the frist experiment by Cori turns into a discussion about farming jobs.
Mods like SPAM and (partially) CAM change the vanilla behavior - there are cap reliefs and a real farm development and industrialization of farming which in vanilla wasn't intendend as farming should be overcome by industries.
I myself noticed that I-R may rise again when your only city in the region ist zoned in great parts - as if to remember to start a second city tile. So, yes, this could be a kind of cap relief when your initial city tile has reached a certain zonal coverage. But I'm not shure about this. It's just something I observed.
Depending on which version or playstyle of CAM you use, IAg can be much easier to deal with than vanilla SC4.
There are also some BSC lots that specifically add cap relief for IAg.
In vanilla SC4, IA capacity can be taken up by CS$ or ID jobs instead, so that your city can outgrow farming at a certain point. Plus adding education can in fact diminish demand for IAg. This is where mods like CAM's rural playstyle really shine for those that want to play more developed farm towns in their regions.