PaulF I can really relate to your story of virgin soil. Here where I live it was never farmed, but there is some clay topsoil. This is just the scanty topsoil formed in the last 10,000 years since the last glaciers scraped it bare. The pH of the clay when I started to garden here was 4.0! And the native vegetation conifers and lichens.
In my first garden I dug as much organic matter as I could get, year after year, still fairly marginal results for vegs. One year I made a raised bed with just organic materials, and it did so much better. Although my garden compost is really the best, where a small amount of the clay has gotten into it on plant roots, SWAG no more than 5% of the clay and in that amount it's magic. So when I hear of soil with 5% organic matter I can only imagine how good that soil was to begin with!
My mom's place, it was one of the first farmlands in this area. 400 years of plowing in the organic matter every year. (there were no chemical ferts here before 1949, so totally organic). The "clay" in her best garden area is brown, not orange, and it's a much better place to start. The color change tells the story, just how much organic was dug in there.
My friend's farm, was intensively farmed by organic farmers for 40 years. Besides organic matter added to the beds, the paths between them were layered in peat every year, and all tilled in at the end of season. It is a really mature farm soil that has great yields (and Lubadub, her tomatoes are huge!). You can still find orangey clay in the thinnest place at the top of the field, when deep trenching the potatoes 2 ft down. Otherwise dig as deep as you like it is a beautiful dark brown.
So my perspective on organic matter may be skewed, but we really can't get too much here.
When it comes to soil structure, things like inoculum and compost tea don't add a thing. Great if you're using promix in containers for example, which is all structure no ferts. This is why I don't have much motivation to the liquid approach, because we need structure first and... yes, it may take 40 or 400 years.
