I'd personally go with the stardew valley system of crop quality, but because PZ has all the nutritional values I'd say just tweak those, unfortunately I think this might just be a power creep! I'd tie farming into the natures abundance system but have the goal of keeping abundance low (pest free) compared to abundance high (infested), foraging your farms cell would reduce odds of plants catching a disease, and similar to foraging provide insects commonly, medicinal plants uncommonly, rocks rarely and mushrooms very-rarely or something of the such. Take away random chance remove frustration, provide more incentive to particular tasks without removing realism!