Azi mentioned Carbon and the confusion that comes with it. Carbon is the hardest part to wrap your head around so I hope I am dummying this down enough. Grab a coffee and you also may read this more than once. If something isn't jiving for you please speak up.
Carbon is similar to calcium in that it is dual purpose too. Calcium is a nutrient and a soil conditioner, and Carbon too is a nutrient and a soil conditioner.
A rootball dissection is the easiest way to demonstrate, and I don't like to open the carbon can of worms until people understand calcium.
The reason is that it's slightly more complicated, but not really, and calcium is an excellent, easy to understand example of something being both food and conditioner.
Carbon is only slightly more difficult, and only because with calcium, both the nutrient and the conditioner come from the same source, and with carbon the nutrient comes from a different source than the conditioner.
The nutrient portion comes from atmospheric CO2, so you don't really need to know anything about that part, it's just in the air.
The conditioner comes from soil carbon, and if you understand how it works now you have the whole package of how organics works.
Plants eat nutrients to make what we grow them for and roots deliver the nutrients to the plant so it can do that.
Calcium sets the charge in the soil and carbon skeletons that are left behind after microbes create acids to dissolve off the carbon they eat, are what carries this charge, like a battery.
So how does calcium charge carbon, and how does that charged carbon get food to the roots?
Well the easiest way is to tell you with a dissection, and I have 2 rootballs right here.
Before we begin make note of the fact that Carbon also holds 4 times it's weight in water too, so it's a hydrator, but for now don't worry about that part. All that does is help you determine how much is too much in soil. You don't want dry and you don't want soggy. So if you are wondering how much Carbon you should add to a mix, the answer is use enough to hold your soil at the moisture level you want.
OK on to conditioning.
That carbon skeleton has a molecular charge that attracts positive ions. If 80-85 of every 100 it attracts, so 85% is a proper mix of Calcium and Magnesium in ratio, So say 60% calcium and 25% magnesium, the charge differential from what the skeleton can attract and it's amount of attraction power left is now down to 15%.
The stage is set by Calcium and magnesium.
So in that remaining 15% K, Iron, Sodium, aluminum, and a few others in trace amounts all fill in the gaps until the skeletal charge is as colse to even as possible, and hydrogen, the quirky cation that can flip from slightly positive to slightly negative fills in the slightest gaps to achieve 100% saturation. The charge is perfectly neutral in the skeleton but with stuff stuck by static everywhere.
So now a root sucks up a K cation and the skeleton gets some space in it as it's now down to 99.99% fully charged, so when the K gets sucked off some other cation gets sucked on. It flows like water but it's actually static cling.
CEC, Cation Exchange Capacity, is how much flow you can add to your soil to deliver more food.
So how is CEC created?
How are these skeletons of carbon formed?
Like this.
2 rootballs and a breather.
Start knocking off dirt and you see roots.
This is the whole 1.6 gal pot and if you look closely there is a thick mat of roots up top in the pot, a less thick cake of roots in the middle, and a large cake on the bottom. Typical of clones in cloth pots.
Top cake.
Middle cake.
Bottom cake.
All the dirt removed. The dark blobs are bark. Thats where CEC is easy to see develop.
Lots of bark nuggets with roots attached.
Lemme type up part 2 now, I need 10 more photos.