Not clearly mentioned here: But you need to Dry the crops to create the inorganic Fertilizer.
And based on your processing level, you need more or less crops.
So far I can tell is skilled 3 requires you 3 crops to be dried.

Processing/Drying
Artisan 2

|-----------------------------------------|
| # | Material | Product |
|-----------------------------------------|
| (0) | 5x Wheat | 2 Inorganic Fertilizer |
| (1) | 5x Wheat | 4 Inorganic Fertilizer |
| (2) | 5x Wheat | 3 Inorganic Fertilizer |
| (3) | 5x Wheat | 4 Inorganic Fertilizer |
| (4) | 5x Wheat | 4 Inorganic Fertilizer |
| (5) | 5x Wheat | 1 Inorganic Fertilizer |
| (6) | 5x Wheat | 3 Inorganic Fertilizer |
| (7) | 5x Wheat | 3 Inorganic Fertilizer |
| (8 ) | 5x Wheat | 4 Inorganic Fertilizer |
| (9) | 5x Wheat | 3 Inorganic Fertilizer |
|-----------------------------------------|

I know its a small sample size, but I was just personally curious with this recipe and actually remembered to post my findings. I'll be posting more on item Processing, as I tend to test these sort of things for my own
records.

With process master 4 i still need 5x Wheat and get 1-4 Inorganic Fertilizer.

Since it's not told in the item description. It'll work for the current garden (fence) and all the directly adjacent ones.
Edit: From an article about farming, it's in a circle around us, so it can technically reach up to 9 garden at once, and we can't have more than 10 apparently.