Good link, Larry!
Here's a simple example of "the soil triangle". But beware: it's a little like USDA Hardiness zones. The soil triangle ONLY talks about "texture". Size of grains. It specifically is NOT about the second-most important factor to garden soil (organic content).
http://www.oneplan.org/Water/s...
Probably our intuitive associations with each "soil texture class" are based on our unconscious assumption that the soil ALSO has a reasonable amount of organic matter from compost or decaying humus.
But the "soil triangle" wouldn't distinguish between rich, fertile, organic "silty clay loam" with 8% OM and abundant soluble and slow-release NPK, vs. sterile inorganic "silty clay loam" that had had every microgram of organics and nutrients leached or burned out of it. (*) The soil triangle is only about texture.
As with USDA Hardiness Zones, if you want to know something USEFUL, you have to combine the soil triangle with OTHER factors, like organic content, temperatures, grade, rainfall, salinity, microbe populations (helpful or disease), mineral nutrient content, pests ...
ad infinitum.
I think this is why people say (wrongly) that "clay soil plus sand equals concrete".
Actually, it should be
"clay soil without any compost really stinks for gardening
and is rock-hard whether or not you add sand or even grit."
Clay without compost is for making bricks and ashtrays.
Adding or subtracting sand or grit is almost irrelevant for gardening
until you get up to half sand and grit, or 70% sand and grit.
Clay plus compost still drains rather poorly -
but clay
plus compost PLUS GRIT AND SAND
drains and aerates a heck of a lot better than just clay plus compost.
Anyway, that's how it works in my yard, even if other people had other experiences. I do mix and "fluff up" my clay-compost-sandy grit and then firm it again gently, and it only lasts a year or two before it slumps down again, but I can grow things in it during those years, and then add more compost and fluff it up again.
(*) I think that if you had ENOUGH organic matter that was
still particulate instead of soluble, the soil triangle would recognize the organic matter - and treat it exactly like crushed granite of the same particle size. But my impression is that you can hardly keep soil organic content above 5-7% unless you're adding compost and mulch several times per year. If you feed microbes that much, they will multiply and eat it faster than you can add it.
Well, faster than I can add it. I have to buy it and wheelbarrow it around, and seldom have more than 1" to add at a time.
