Salem

Although I am pretty sure productivity of tilled fields is in no way related to the biome it is placed upon, I just wanted to make sure

So, is it?

PS. Imho productivity bonusses for different (greener) biomes would be logical.

Nope.

What he said.
AFAIK you can still place fields over paved ground for extra lols.

I wish there was at least some correlation to soil "quality" and the biome, or perhaps different crops would become differently aligned based on some pre-known factor, for instance:
This area produces foraged lavender blewits which are high in mercury, therefore pumpkins grown in this area will become mercury aligned.

Although the whole farming purity system changed last year didn't it, all depends on the clay and the water for the trees for the wood for the compost or something doesn't it.