When you designate farmland, a preset number of farmers are allocated immediately.
While the farmland is still being created. At this point, you are unable to set how many villagers you want to be assigned to this area.
Especially early on, when every worker counts, it’s unfortunate when a whole bunch are just classed as farmers and go home for the winter because the ground is frozen - and you cant do anything about this (except for destroying the farmland construction)
Another thing - if you halt construction on the farmland, the farmers remain farmers, and will sit around inside the house playing dice forever and ever, until you turn the construction on again. Since you dont see them you are left with mysterious invisible non-productive villagers.
Farmers don’t construct fields, that work is done by your labourers. Farmers only do the last preparatory work before they start planting. Yes, it can take time if you have large fields and yes, they will stop in the winter because the ground is frozen.
As you put down the initial field dimensions you can see how many farmers will be allocated once the field is ready for them to start working on it.
As soon you plan a field the workforce for the farmers is incread total!
So if u plan one ore more fields (even if u stop the bulding process), the farmer workspace is increased!
So, if you plan your fields and for example setup 10 field 12x5 (need 5 workers) your free workforce is imidaly decreased by 50!
Thats not fine - even if u dont know this u can run into deatly workforce traps if u plan a lot of field in prupose to use the in a far future … the plant farm still decrease your workforce fpr nothing!
Go to your worker overview and untick the automatic assignment. Then you can reduce the farmers to the amount you want. Like 0 while the farmfield ground is still freed from trees and stones by labourers. After that you assign manually as many as you can afford. As soon as your field is ready to be farmed you can set the number of farmers for that field in particular and toggle the automatic assignment back on. The ingame assigned number of farmers per field is usually to high. If you can clump your fields close together you can get away with much less without crops rotting.
I’ve found that 3 farmers per 72 tiles work like a charm. Usually I start my fields with 12x6 early on and leave room between them to expand them later as needed (adding another 12x6 tiles). Currently I’m running a game on 3 fields with 12x18 for turnips/peas/wheat and 1 field 12x12 with 2 years flax/clover and 1 year maintenance/clover. No noteworthy losses to crop disease, only the unavoidable heat/cold stress.