It’s Korean Natural Farming. It’s really a philosophy of organic gardening. One of the key aspects of it is making your own fermented plant nutrients by using local plants, and indigenous micro-organisms.
I got interested in it during a war with PM. One of the primary KNF inputs is Lactic Acid Bacteria Serum, or LABS. It really worked on the PM, so I started reading more about it. I’m making some Fermented Plant Juice, FPJ, as we speak.
There are some threads about it here on OG. Here’s one of them.