Meaningful trade (non-trivial to transport goods over distance)
Item decay (produce has a finite lifespan and will rot)
Biomes and weather
Survival mechanics (PCs, NPCs and animals need food)
So prerequisites are all things we expect to see anyway.
How this factors in to advanced farming:
Farming isn't about being able to grow something, it's about being able to grow large quantities and produce a surplus.
For this to be important we need only that everyone needs food and supplies, and that those things can't be stockpiled forever. So there's demand.
Advanced farming could be about maintaining supply in difficult conditions.
Growing crops in a climate where they might usually struggle. Managing what you grow to survive harsh weather.
If certain biomes make some crops hard to grow, and it's difficult to transport produce over long distances, then good farmers can be in demand.
Add in some mechanic for altering the soil over time and we could really be on to something. Depending on irrigation, how you cycle crops, what you grow, what you put on the soil, how you work the ground, wildlife, etc. perhaps you can make the soil better adapted to growing certain things than it would naturally be.
This lets farmers build something up over time, make progress and get to where they have a much more "powerful" farm than they did before. Perhaps some ingredients which are highly prized can only be grown in useful quantities on a highly developed farm.
It also creates a stronger connection between the players and the land - not just the farmer but those who need their produce.
Finally, of course, it may make unscrupulous nobles cast envious eyes on that land if they need it, so extending far beyond simple gathering mechanics.