Roots of many garden vegetables penetrate 8 to 12 feet deep. I suppose that the fungi are growing right along with the roots. So if I till super deep, say 6", then that's still only 4% of the soil volume that the fungi and roots are using. And if I do routine cultivation of weeds, at 1" deep, then that's disturbing less than 1% of the space used by the roots/fungi.
And it seems to me from watching them grow, that fungi are self-grafting, and self-regenerating. Any part of the fungi can re-grow itself and can graft itself to any of it's kin with which it is compatible.
Roots do go down deep, but the vast majority of biological activity in all soil is in the top few inches, what a soil scientist would call the A horizon. The limiting factor for deeper activity is Oxygen availability. As far as I know, every known mycorrhizae species found so far is aerobic.
This thread interests me greatly because I just finished reading Gardening When it Counts, growing food in hard times. The thing that got me to read it is the fact that I have been sowing my seeds to close together and never thinning and I need to stop doing that... Of course I already knew that and continued to do it anyway. My he book is billed as the antithesis of John Jeavon's How to Grow More Vegetables and Mel Bartholemew's Square foot gardening. When I do space out my seeds I often have consulted Mel and John about spacing. I have no complaints yet (haven't tried them yet) about the books spacing recommendations- I intend to try them for a change. Nor can a fellow (me) who has imported 8 dump truck loads of sand so far complain about the importation of Sandy soil by someone claiming to teach us how to garden in hard times.
Amendments mentioned in the book I question. Limestone powder, gypsum, and lime added to the complete organic fertilizer. I garden on Glacier Lake Missoula's lake bed. Probably enough like in it.
Kelp I've used it. Probably will keep using it but it probably isn't worth paying for. It doesn't grow around here.
Comfrey- never been convinced to grow this. Still not.
Seeds- I prefer improper seed sources thank you your recommendations will be mostly ignored. I will probably continue to save seeds from things I should not and to buy seeds from the most interesting genetics I can get not the most productive or uniform. I'll trade seeds to keep my stuff from getting inbred if I can.
He throws a back handed compliment to the Ruth Stout method. He says it's second rate but may be good for the elderly like Ruth. I am lazy, if I had the mulch I would try Ruth's methods. Frankly I have plenty of land for garden expansion. Unfortunately I've not yet found a cheap enough source of enough hay or straw to garden by Ruth's methods.