That mushrooms and berries are invisible and have to be gathered by random chance AND decrease the soil quality on each find is a bummer.
There are still other threads about soil quality, but I suggest an overhaul of the mushrooms and berries system:
Make it like the herbs system, search for mushrooms and berries and they become visible and can be gathered with a sickle.
And ofc the soil quality should not be decreased by finding stuff at all ...