Is charring really an effective treatment for ground preservation of wood?

It’s interesting reading the interpretation of the study from the OP. I read a lot of them and it’s true, they have to be read with some context. But this is particularly interesting because this was largely done before there was any vested interest in chemical treatment. I mean these posts and treatment tests were done in the 1950s! The more recent tests don’t even include ACQ which is the most common treatment. This is old and presumably less tainted data.

Additionally the posts in most of the study were the same type of wood in the same place. That removes a lot of variables. I really really actually like this study.

The most interesting thing- by far- in the data table in my opinion is that the Osage orange had no rotten posts - after 70 years! In freaking Oregon! Unbelievable! I planted a few hundred pretty close together to try to get some straight poles in maybe 20 years. This seems like the logical step for ground contact. I’m throwing in some black locusts seed this year in the “patch” because it’s awesome but we’ve had issues with borers that might limit the usage.

Well I'm not a trained pro or a PHD but I can tell you by experience that charring wood well help it last longer, the old people in the mountains of Tenn. did it all the time. They well tell you the spring is the best time to do it because the sapp  comes to the surface in the pine trees as the tree cools and remains there and acts as a barrier against water and some insects. I have seen this proven out over time and it does seem to work. But I will add this process seems to work much but on pine, ceder, white pines and trees that have type of sapp.  

Hey Rufus, when you say salt do you mean regular sodium chloride or sodium salt of boric acid (borax)?  I would think borax considering salt increases water retention, though I have read regular salt can be beneficial in preventing checks and shakes (cracks) when drying out green timber.

Hello;  

 This has been working for me::  Treat post  with termite oil , (which can be replaced used crankcase oil from diesel engines). Best to soak in a bucket for at least a week. Then dry in sun , rotating , until surface is mostly oil free. Now wrap bottom part of post in rolled roofing material, secure with galv nails or better. This of course works better if post is round, You can also use old roofing shingles, in layers such that water runs off. Single layer should extend above finish grade by 6 inches. I use fiber glass reinforced shingle material. This stuff can take direct sunlight for decades. On the bottom  of post  I use a block of 1 inch thick plastic cut to match post cross section. Screw nail it in place. The shingle material wrap should extend right to bottom of plastic cap. The idea behind this method is to keep the anti termite oil from leeching out, drying out from contact with soil.  Set post on a brick or flat rock, backfill with gravel. I realize used crank case oil is a bio hazard, but if you do use it thin with paint thinner 50% and let it completely soak in before wrapping the post. For this use,  the blacker the diesel crank case oil is,  the better ...hopefully with shingle wrap the oil will stay inside the wood post for many years and not get into the ground at a rate that is hazardous.