this reminds me of how kimchi and is made in korea - they put everything in a jar sealed it (wax maybe) and buried it. Sauerkraut is fermented similarly but I don’t know if the germans ever buried theirs.
Kimchee or Kraut is best made at 65 degrees in a crock with a fermentation airlock. Earth temp is around that. Using sea salts and mineral salts like himmilain salts provide trace minerals that activate the enzymes created with fermentation. It will keep for over 9 months without a fridge.
Half chopped cabbage, half mixed veggies is great. Mix 2 parts with one part sour cream and its a great chip dip.
Eat from 2 weeks to 6 weeks for maximum pro biotic effect.
It is a great way to keep non root crop veggies as well as root crops.
Easy to do and learn, get yourself a “Perfect Pickler” kit for 20 bucks comes with a how to DVD.