yes the term humus is interchangeable w/ organic content for most folks - have never heard of any actual measurement of humus, which is almost a soil process rather than a component - see this for some insight on the various stages and complexity of humus

Bill

Humus is the residual organic matter left by the soil microbes, the stuff they would treally prefer not to digest if there is better stuff available. To measure it easily take a clear one quart jar with a tight fitting lid and put 4 inches of your soil in that jar. Fill the jat with water, put the lid on tightly, and shake that jar vigorously, then set it aside for about 24 hours. Your soil sample will settle out with the largest and heaviest soil particles on the bottom with the lighter and smaller going up according to size and weight. Humus will be on top, with some floating in the water above the soil. That amount of humus will tell you about how much you have in your soil. Divide the the level of humus by the total amount of the soil sample, in inches to get the percent, ie. 1/4 inch of humus divided by 4 inches equals 0.0625.

kimmsr: if that is how to measure humus, how does one measure soil organic matter? Regards, Peter.

Peter, humus IS the soil's organic matter! Hop over to the Soil forum, thread titled: "Manure and Composted Manure". Various official humus definitions will be found in a reply there.

Martin

In the soil, organic matter is dissolved and absorbed by microorganisms utilizing the nutrients and energy for their own metabolism. Their activities convert most of the organically bound nutrients back into a mineral form which is usable by plants and other microbes. The undigested portion of the residues accumulate as humus. However, humus is not completely immune to decomposition. Microbes will eventually recycle all the elements in humus back to where they initially came from, even if it takes a millennium to do it.

Some of the components in organic residues are much more resistant to decay than others. Carbohydrates such as sugars and starches will decompose faster than other carbohydrates such as cellulose and hemicellulose. Fats, waxes and lignins are the most resistant to decay of all the organic components. Proteins vary in decay resistance but are generally more resistant than sugars and starches yet more easily decomposed than all the other components.

Although many of these components exist in humus, the degree to which they exist in the organic residues plays a role in the quantitative accumulation of humus. Materials that contain a high percentage of easily decomposed components such as sugars, starches and proteins are, for the most part, assimilated back into the living biomass. Although the energy and protein provided by these residues help in the creation of humus, the ratio of the mass and weight of the residues to the measure of humus produced is relatively high (i.e. only a small amount of humus can be created).

Materials that contain a large percentage of lignins, cellulose or other biologically resistant components have less to offer plants in the way of recyclable nutrients but contribute significantly more to the formation of humus.

Different plants inherently have different ratios of these organic components but variance also appears in the same plants at different stages of their life. Green leaves from deciduous trees, for example, have a very different analysis of proteins vs other components than their dry, fallen counterparts. At the young, succulent stage, organic matter from this source would not contribute very much substance for the accumulation of humus but would benefit more the immediate needs of microorganisms and plants. Whereas, near the end of its life, the rye plants would add little to the nutrient needs of plants and soil life but provide more raw materials needed for the formation of humus.

During humification not only are the organic components altered by microbial processing but the ratio that existed in the original residues is changed. Figure 4 illustrates how the balance of components in straw changes from decomposition. The increase of some components and decrease of others is not magical. The nutrient needs of microbes involved in the decomposition process are taken from any available sources in the soil and reflected in the analysis change from raw material to compost. As the compost humifies further the changes become even more pronounced.

Biologically resistant components such as lignins, fats and waxes are structurally and chemically changed by microbial processing. Other biologically resistant carbon compounds are created by microorganisms as by-products of their decay activities. These decay resistant compounds are what humus is made of. This is not to say that humus is immune from further decay, but its resistance to decomposition is at a level that enables it to exist for decades if not centuries as a soil conditioner, a habitat for microbial life and a vast reservoir of plant and microbial nutrient.

Germ's cut-and-paste were just a small portion of a much larger and thorough definition of humus. The full thesis, in its entirety, is linked below.

Martin

Here is a link that might be useful: Humus: Still a Mystery

Well it made more sense to me than anything else that was posted.

Arbitrarily changing dictionary definitions is not widely accepted. Quoting such definitions is accepted. Linking to copyrighted material on the Internet is OK, printed verbatim without credit is not. And, passing such off as one's own work is plagiarism.

Martin

I thought I had that on the bottom of that post, but I see now I didn't. Not that it's any of your concern. I wasn't trying to pass it off as mine.

Ok, let me post it now: http://users.ids.net/~nofari/tnf_hums.htm

By Paul Sachs

Here is a link that might be useful: Humus, Still a Mystery

No problem, Germ, you just saved yourself and others some headaches if someone reported it to GW, something which has been done a few times! They may be especially sticky now with the new rules.

Martin

hmmmm ... interesting that you guy's didn't seem to notice that the first answer in this thread linked that article in it's original location, yet you all go on to ignore
"The term "Humus" doesn't really describe anything specific. Its like using the word "dog" to describe a German Short Haired Pointer."
and try to claim humus is simply "organic matter", then link the same article?? and kimmsr: " the stuff they would really prefer not to digest if there is better stuff available??!!!???

quote:
"SUMMARY
The popular scientific definition of humus is "A more or less biologically stable, dark, amorphous material formed by the microbial decomposition of plant and animal residues". It is difficult to visibly differentiate humus from organic matter in other stages of decay. Compost, well rotted manures and peat are not necessarily humus. However, at some hard-to-define point, all of these organic materials will contribute immeasurably to the humus content in the soil.

It is not realistic to think that one can quantify or qualify humus production from contributions of organic matter to soil. There are too many factors that control its formation and existence in the soil environment. One can only assume that cultural practices that both minimize the depletion and contribute to the formation of humus will maintain the best possible level of soil humus for each individual environment."
/quote

Bill

Bill, if humus is organic matter how would one get humus in the soil if it is not realistic to quantify humus production from contributions of organic matter to the soil? Where does humus come from?

In summery, humus is difficult to define let alone measure. I would suggest not worrying about placing a number on the amount of humus in your soil. Instead decide if you have enough to provide good soil structure (arguably the greatest benefit of humus) and adjust your organic additions accordingly.

It appears that some are trying to change or alter the definition of soil humus. Directly quoted definitions of the SCM forum were implied as to have been wrong. Take your pick below of which to accept but be prepared to explain why others are not acceptable.

Martin

Here is a link that might be useful: Humus Definition

Martin, as I said in the beginning most folks equate the term humus with organic material - and as the professional linked a number of times here points out, humus is a very nebulous substance that defies description and measurement because it has to do w/ soil processes which are never really complete nor in stasis - nature isn't as consistent and simplistic as humans would like and isn't always amenable to single sentence definitions or explanations!

does "humus= A brown or black organic substance consisting of partially or wholly decayed vegetable or animal matter that provides nutrients for plants." really say anything? isn't that also "compost"? or even many bagged fertilizers?

so, yes kimmsr, organic material contributes to the formation of humus, to varying degrees under various conditions, but quantifying the process appears impossible - if you think that adding X amount of "organic material" to your soil provides some specific amount of "humus" I have no problem w/ that, as long as you don't tell me the same amendment will obtain the same result in my soil, or Peters or anyone elses, and as long as you understand the extreme range of possibilities affected by the type of organic material, other soil conditions, including microbial populations, and the climate and treatment/use of the soil

the original questions were:
"How is soil humus measured?"
and "is this just a misleading way of saying "soil organic matter"?"

the answers are that it isn't measured or measureable, although soil labs will call their determination of organic content "humus", and I provided the best link I've ever seen concerning 'what humus is' so Peter could get a better understanding of what it is, does, and is a result of

Bill

Peter 6, by now your question has been answered although it's not obvious at first glance. The true answer is that humus can not be measured. The reason that it can not be measured is that nobody here knows what it is that they are looking for. The no-till faction will claim that whatever it is can't be in their soil since they only put stuff on top. Those who till will say that they didn't put any in so it can't be there. Corn farmers in Kansas might look at you sort of strange and tell you to get off their property. Since it does seem to be something recognized by a great number of rather credible institutions, undoubtedly for centuries, it must exist but whatever it is is obviously above the understanding of most viewers here.

Martin

Enjoyed your pithy summation Martin.

Thank you all. I didn't realize that it was such a good question. Now we know what I had long suspected that soil tests that show humus measurements and people who think that humus and soil organic matter are the same thing are misguided -- innocently so of course. Regards, Peter.

Here's how humus and s measured https://www.biology-fieldwork.org/a-level/fieldwork-techniques/abiotic-factors/soil/#primary-nav