Crop Quality Question

I’m new to the game and could not find a current answer for my question on the forums. Is the quality of crops (e.g. pumpkins, cereals, etc.) determined by the initial humus used to prepare the field, the fertilizers added after planting, or a combination of both? For example, if I use 0% purity seeds with a 10% humus for field preparation will the seeds be >0% - >10% purity regardless of what fertilizer purity is used?
And is compost bins purity only controlled by wood for construction and worms? Does what you put in the bins matter for the humus quality?
Thanks
And is compost bins purity only controlled by wood for construction and worms? Does what you put in the bins matter for the humus quality?
Thanks