The single largest problem with humus (and humic acid) is all the misinformation that is in circulation and part of that is calling things that are not humus or humic acid, humus or humic acids.
Organic matter in the soil is often called humus, but it is far closer to being compost rather than humus.
Many people are now selling organic materials and calling these materials humus, but what they are selling is more like compost.
This misidentification continues because "experts" continue to use the wrong terminology when they are talking about soils and how to improve those soils.
Humus is not something you can work into the soil, the very nature of humus is that of complete and total decay of organic matter, humus occurs only at the molecular level, so our eyes can't even detect it.
Humus, being molecular in nature means you would be hard pressed to hold any of the stuff in your hands since to find it you first have to locate organic matter that has been completely decayed, solid matter can not be humus because we can grab a hand full.
Compost is solid matter that is going through the process of decay, it is useable by humans because it has not finished the decay processes, once it does then it will be out of our sight and touch.
Humus can not come from coal because coal is plant material that became compost like and was then put under high pressure, which causes heating, and that turns it into coal eventually.
To think you could take coal and grind it up and get humus from that ground up material is showing lack of understanding what humus is.
Coal doesn't decay, if it did we would not be able to mine it and burn it as a fuel.
The deeper you look at everything represented as humus, the more you find that what ever is being called humus is most likely not humus but some form of organic matter.
Humus has been decomposed so much that it actually is no longer organic matter, it came from organic matter but since it has been broken down into molecules or atoms, it is no longer organic matter.
If you were to call humus "derived from organic matter" you would be closer to it's true identity.
Plants and animals contain many of the same minerals and other nutrients (Like N,P,K as an example) we use most of those minerals and nutrients to build the cells and other stuff that make our bodies and fuel them.
Humus would be those minute pieces (minerals and nutrients) in the same forms that plant roots or animal digestive tracts take in so the organism will survive and grow or maintain the current structure.
Humus doesn't actually add "organic matter" to the soil, this is one of those misconceptions that has been bandied about for so long that many people say it as a fact, but it isn't. (sort of along the Urban legend type thing)
Humic acid is another item that has many misconceptions running around about it.
Humic acid doesn't stay humic acid, it gives up electrons quickly to become stable, but in doing this it no longer is an acid it becomes another molecule floating in the soil.
Humic acid is formed by rain water passing through humus, it takes on electrons from the humus molecules thus changing those molecules the water robs the electrons from.
Like Humus, Humic acid reacts rapidly once formed so it is here then not here, snap your fingers and you can get an idea of how long humic acid exists as humic acid.
It is the rapidity of change in these two substances that have made it so hard to study or even investigate, only recently have we come up with the right tools to be able to do proper study of the properties of these two keystone items of the soil.
(keystone items or beings are those that are so critical to the well being of the planet or ecosystem (soil is an ecosystem) that without them, the whole system falls apart).
Humans have a need to quantify everything which is probably one of the reasons there is so much wrong info floating around the different media, we have an innate need to be able to describe everything, it is what allows us to understand anything.
If we don't know the real facts of how something works we will either experiment to gain knowledge about that which we don't understand or we will invent what appears to be knowledge.
It is these human traits that push us forward in the quest for knowledge but these traits are also what lead us to make stuff up so we sound like we are knowledgeable.
If you want to find humus you have to look for it in a laboratory setting since out in nature it disappears almost as quickly as it forms.
This is because it can't exist until the organic matter that creates it has to be completely taken apart by the processes of decomposition, only then can humus come into being.
So as the last bits of say a tree limb that has a dead lizard gripping it disintegrate into those components that made up the solid parts of the limb, you see humus be created.
Once humus is created, it immediately binds with those molecules and atoms that make up the inorganic parts of soil at that instant, humus is gone.
We now have instruments that allow us to locate where the humus went and what it turned into and those instruments identify these substances as organic because they will contain the carbon atoms that were freed when the tree limb decayed away from the actions of bacteria and fungi.
This is why humus is such a mystery, it is still almost impossible to take any sample of soil and locate that substance known as humus (or humic acid since both seem to work in similar fashion).
However, if humus didn't exist, ever, then we would not have rich soil to grow plants in and those plants that did sprout would be lacking much of what makes them up.
Experiments have been done that were designed to locate, isolate and congeal into a solid, measurable form, the ions, minerals and elements that make up humus.
Most of these experiments have either failed from their design or the substance was found then it changed molecularly enough to not be the desired form humus any longer.
This is the type of investigation that creates bald scientists, they most likely pulled all their hair out from frustration.