Humus Does not Exist – Says New Study

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Robert Pavlis

As a gardener we all talk about humus. Some of us even buy humus soil, and humic substances like humic acid and fulvic acid. We add compost to gardens to increase the humus level in our soils in the belief that humus is good for soil. Good garden soil is dark because of the high humus content.

If there is one thing all gardeners agree on, it is that humus is good for the garden – right?

Maybe not!

Science now says our beliefs about humus may be wrong. In this blog I will review some earth shattering news – or is that soil shattering news?

humus Contentious Nature of Soil Organic Matter
Humus Does Not Exist – Says New Study: The Contentious Nature of Soil Organic Matter, by Johannes Lehmann & Markus Kleber, published in Nature

What is Humus?

I have answered this question in a previous post,  written in 2013, called What is Humus? You can review the previous post for more details, but I will summarize key points here.

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200 years ago soil scientists noticed that good agricultural soil was black and in an effort to better understand this black stuff they devised a method to extract it from the mineral components of soil (ie the silt, sand and clay). They treated soil with a strong alkaline solution of pH 13. This procedure pulled the organic component out of soil so they could study them.

Over time, this black substance became known as humus.

Humus has some very unusual properties. It is composed of mostly carbon and some nitrogen – not that unusual. The unusual part is that humus is very stable. In fact it takes 100 years or more for it to decompose. Microbes can’t seem to digest it even though microbes can digest just about every other organic material, including oil.

The treatment with the alkali produces two main components which are called humic acid and fulvic acid.

Decomposition Produces Humus

Lets try to understand the complete process of what happens to organic material in the garden. Organic plant (and animal) material is added to the soil. It might be added directly as leaves fall to the ground, or it might first be composted by a gardener and then added to soil. For the purpose of this discussion both processes are the same. Once in the soil, pieces of plant material are decomposed into large molecules like proteins, and carbohydrates by the action of microbes (bacteria and fungi mostly).

Over time the microbes break the organic material into smaller and smaller molecules and in the process nutrients are released for plants to use. This process takes about 5 years on average. For more details on this see Compost – What is Compost.

At the end of the process, most of the organic material has been used up by the microbes and what remains is the humus. Humus is a substance that microbes can’t seem to digest, so it builds up and remains in soil for many years. It is extremely stable, some claiming it sticks around for 100 years or more.

The black color we see in good soil is due to a mixture of organic matter that is decomposing, and humus. It is mostly humus.

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Humus – Does It Exist?

The decomposition process described above has been the accepted truth  for many years and was the accepted story in 2013 when I wrote my last post. But scientists have always had some issues with this story. Even 100 years ago some scientists questioned the existence of humus.

Humus could not be characterized in soil. That means that scientists could not analyze humus while it is in soil. They could only work with it after extraction at pH 13. A pH of 13 is very alkaline and at this pH all kinds of weird chemical reactions take place. Nobody could say for sure that the humus in soil was the same humus being studied after extraction.

Why Is Humus So Stable?

The decomposition process happens because microbes break apart plant materiel into smaller and smaller molecules and yet humus is immune to their digestive processes.

What else do we know about humus?

Humus is made up of very large molecules but over many years of study, no one has been able to clearly describe the structure of these molecules. That is odd given that with today’s scientific tools we can establish the molecular structure of just about everything. Humus is still defined as “a large, undefinable, quite variable molecule made up of mostly carbon and hydrogen” – that doesn’t tell us much!

Scientists don’t know what it is, and can’t explain why it is so stable.

Even more interesting is the size of the molecules. Keep in mind that microbes break down organic mater into smaller and smaller molecules. Why is it then that at the end of such a process we have very large molecules? These molecules did not exist in the plants when the process started. This means that they either formed on their own – which would be rare in nature, or they are created by some biological process which is completely unknown.

No one has been able to explain why and how the large molecules are created.

Humus Does Not Exist!

A very interesting paper was published in Nature, December 2015, by Johannes Lehmann & Markus Kleber, called “The Contentious Nature of Soil Organic Matter”, ref 1. For those not familiar with the magazine Nature, it is one of the top scientific magazines that tends to publish the creme-DE-la-creme of new discoveries. It is extremely well respected.

I’ll explain the details below, but what this paper says is that we have been looking at humus the wrong way for 200 years. Humus does not exist in the soil. Humus is created during the pH 13 extraction process. The strong alkali creates humus.

There is organic matter in the soil. When it is treated with a pH 13 solution, it goes through a process which creates the large humus molecules.

The New Decomposition Model

Using the information provided in the above mentioned paper, I’ll re-describe the decomposition process.

Organic plant material is added to the soil. Once it is in the soil, pieces of plant material are broken into large molecules like proteins, and carbohydrates by the action of microbes.

Over time the microbes break the organic material into smaller and smaller molecules and in the process nutrients are released for plants to use.

Organic matter seems to decompose slowly for two reasons;

  • molecules interact with soil, in effect hiding from the microbes
  • microbes build large molecules making the process start all over again

Large molecules of organic matter interact with soil more than previously thought. In fact the soil tends to hide the organic matter from bacteria to some extent, slowing down the decomposition process.

The second important point is that microbes use small molecules and build them up into large molecules, just like plants do. They take simple sugars, nitrate and phosphate and build proteins, DNA and carbohydrates from them. This is not new information, but the paper suggests that this process is much more significant then we realized. Microbes slow down the decomposition process by making it start all over again.

At any given time, soil contains a wide range of molecule sizes – The Contentious Nature of Soil Organic Matter – the title of the research paper.

There is a steady stream of large molecules entering the system when new plant and animal material is added to soil and by the death of microbes. This organic matter is constantly being decomposed into smaller and smaller molecules eventually turning into simple nutrients like nitrate and phosphate, as well as carbon dioxide.

Soil does not contain humus, as previously defined. There are no large stable humus molecules and there are no humic and fulvic acids. Humus and the associated acids only exist in the test tube after soil is treated with a pH 13 solution.

What Does This Mean For The Gardener?

It does not change a lot for the gardener. We already knew that it is important to add organic matter to soil – that has not changed. We know organic matter feeds the plants over time. We know it improves soil structure by creating aggregates.

As explained in my post What is Humus?, you can’t buy humus even though a lot of people sell it. What they are selling is just organic matter with a fancy label and probably a higher price tag.

Humic Substances

The term humic substance is used as a catch all for a number of products including humic acid and fulvic acid.

We now know that these are created in the extraction process and are therefore man-made chemicals. Contrary to common belief, humic substances are NOT organic (in the sense of organic gardening).

Do they work? Do they add any value for plants? Sounds like a topic for another post – but the short answer is that their may be some value to them – but the scientific evidence supporting a real value in the garden is weak at best.

The Scientific Process

There is a lot of negative press these days about science and the scientific process. Everything is controlled by Monsanto, and all the scientists are paid to lie about their results. Anyone with half an ounce of common sense knows this is bull.

Science is not always right. With humus they were wrong for 200 years. Part of the reason for this is that soil science research is not funded very well – but 200 years is a long time.

The issues about humus were raised as early as 1888 (ref 1), but they were dismissed. They were again raised 50 years later and were again dismissed. Now it seems that there is more support for the idea. Part of the reason for this is that we now have better technology which should be able to detect humus in soil, but it can’t find any.

The important point of all this is that science research is a self correcting process. Over time mistakes are corrected by new studies. The system does work. Over time science does reach the right conclusions. We have just observed for the first time, the gravitational waves predicted by Albert Einstein in 1916. Science may be slow at times, but it is much better than the alternatives.

Is this the end to the humus story? Probably not. The paper I am discussing is very new and not all scientists agree with it. It is quite possible that in another 2 years I will write about humus again and change the story, but I don’t think so. The issues with the old humus story are now clearly explained, and the new theory fits the data we have.

This paper discusses reasons why the new view has not been adopted more.

References:

  1. The Contentious Nature of Soil Organic Matter: http://www.nature.com/nature/journal/v528/n7580/abs/nature16069.html
  2. Photo Source: The Contentious Nature of Soil Organic Matter
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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

70 thoughts on “Humus Does not Exist – Says New Study”

    • There is nothing in its list of ingredients that makes it special. It is essentially compost, with a bit of fertilizer added.

      Reply
      • you are correct and they play the angle it’s organic but by looking at the N-P-K sources you can tell it’s not certified organic. In fact the total OM per bag is not very high. it’s a soft coal from a southwest quarry. A well aged compost will deliver more pounds of OM in comparison. In addition the the use rate of 200 lbs per 1000 sq ft is irresponsible. That’s 10 lbs of actual N per 1000 sq ft. Of course most will end up in run off water and contributes to pollution. If a growth response is noted it’s from the N and not the humates.

        Reply
  1. Humus provides safe haven for bacteria which inturn give off chemicals that are helpful for root stimulation aiding uptake. People should think laterally with a micro ecosystem, and not cut it up into small packets of time frozen facts. Science as we know it does not see the whole picture and will never understand the truth.

    Reply
  2. Why does humic testing by farmers always show significant benefits especially water holding capabilities in the southwest and theses are evident even if there not useing bio charged carbon.

    Reply
    • Soil contains organic matter. This is the material that is measured in humic testing. Organic matter holds water.

      Reply
      • I put 30 tons good compost to the irrigated acre on organic pecan farm totaling 3,000 tons over three years it dont hold water as good as 3 ton bio charged carbon to irrigated acre just wondering why. I have to water more often with the compost. But there both really good products for pecan trees.

        Reply
  3. Very interesting information until the very end. Is science always right or is it self correcting? It cannot be both at the same time. Simple common sense will tell you that if it corrects itself it was wrong in the former. To insist that scientists do not skew results to fit desired outcomes required by funding is nonsense. Science has been wrong too many times to even begin to list. I trust science to arrive at the truth, eventually but there are many current instances where scientists practice backwards science. That is, to start at a desired conclusion, cherry pick data needed and delete opposing data in order to justify the already drawn conclusion

    Reply
    • It is self correcting until it gets it right.

      We have to remember science is done by people, and just because they are scientists does not make them intelligent and able to make the right decisions.

      Reply
  4. With all these comments and/or arguments I have to rely on just what my daddy and all other farmers used to do and that is go out in the field and collect as many cow patties and mix them into the garden and throw away all your peelings into the garden and call it good……garden always did very well and no one had to spend any money…..they did not have a tiller so had to hoe hoe hoe it all up…..people try to make it too easy…..I think that we should go back to the old days when farmers used what they had and God did the rest……Thank you but no thanks…..

    Reply
  5. “The issues with the old humus story are now clearly explained, and the new theory fits the data we have”

    Which is exactly why I agree with you, and concur that you probably won’t be having to change your mind about humus again. Thanks for the information. It’s going to let me move on to the task of actually fixing the soil in my lawn, without the distraction of wondering if I’m actually doing the right things.

    Reply
  6. After reading through the article, paper, and much of the subsequent conversations I would like to make a few statements before adding to the topic.
    1. The scientific process does not “prove” anything, rather it provides evidence for or against a stated hypothesis. When enough evidence has been compiled theories are formulated.
    2. It is important to note that the paper is a “perspective” journal article. This means that the authors have taken the evidence available and provided an alternative interpretation. They are arguing against the existence of humus. You may agree with them but you cannot say that humus doesn’t exist, of course you also can’t say that it does. This kind of ambiguity is far more prevalent in science than most people realize.
    3. There is a disturbing amount of fraudulent and unethical behavior throughout the scientific community. Unfortunately we humans are flawed animals. I have been around fraudulent scientific practices both in the academic and private sectors. What’s worse is that there are significant consequences for anyone that blows the whistle. Therefore it is equally incorrect to either trust or distrust all scientific evidence. Finally, regardless of how reputable a journal is (Nature, and Science are the two most) they are not immune to publishing fraudulent research. The Korean scientist that claimed to have cloned human embryonic stem cells is a perfect example, his stain on the scientific community was published in Science, TWICE.

    Now, on to my contribution…

    I’ve been working for a humic products company for almost five years. I’m a scientist (plant biologist) and Certified Crop Advisor in the southwestern United States (Arizona, California), and I DO NOT endorse the use of humic products. As you can expect I’m not long for my position. In my experience the addition of humic acid has shown positive results, but not always and there seems to be a good explanation for this. Growers that till heavily and add little to no organic matter to their soils benefit the most from the application of humic acid. The growers who don’t are the ones whom have a well crafted fertility program, or fantastic soil to begin with, like the black earth soils of the Midwest. It is easy, with the given evidence, that the grower can get all the benefits of a humic acid product through good cultural practices. It costs the grower a lot less and yields other benefits like disease control, and erosion control. By good cultural practices I mean appropriate tillage, crop rotation, cover cropping, and amending with rock dusts and good compost. I’ll reemphasize GOOD compost. Because of the scale that commercial composting companies work they can struggle to find a diversity of inputs to make their compost. They also require a certain amount of turnover (I don’t mean turning the pile), so if the compost is not quite done it gets sold and the customer gets a bad product. Lastly, I think that microbial inoculants fall into the same category as humic products. There is evidence of their efficacy, but again it is not consistent. I’ve witnessed the same trend, soil quality goes up, effect of microbial inoculant goes down.

    P.S. biochar is a bunch of bull****. I could go on, but I think I’ve already said to enough.

    Reply
    • I agree with your points.

      I also agree with your statements about humic substances and microbes. These are not needed in home gardens, and adding organic matter and mulch are better long term.

      Reply
  7. Humus is an artifact of early science and is reminiscent of phlogiston, a substance once invoked to describe combustion, now known to involve the exothermic formation of compounds formed with the element oxygen.

    Science is indeed self correcting, although it can be ignored and disputed, often by those who don’t understand it or have a distaste for its conclusions, as in the revelation that mankind descended from ape-like creatures.

    How apes form beliefs and demand socially acceptable ideas may inform the problem of why science is attacked with the intellectual equivalent of a femur bone. Can managing reproduction with the requirement of a simple license, like that required to drive a car, help the situation? I think we should try.

    Reply
    • Hmmmmm. A license required to reproduce? Where are you? China? N. Korea? You’re certainly not American

      Reply
  8. Hi Robert, I’d love to link to this article, but I just thought it would be improved a bit if you could made the distinction a little clearer about when microbes turn smaller molecules into larger ones — that this is when they are building their own internal structure (DNA, proteins etc.), and when they turn larger ones into smaller ones — this is their conversion of food into waste products. So they are doing both at once, with the emphasis on the latter, and it’s only when they die that they add a few larger ones back in the mix. At least that was my reading of the Nature article. Cheers!

    Reply
    • That is sort of correct. They also need to form larger molecules when they form enzymes which are needed to convert the food.I would be surprised the emphasis is on the latter because that would be a very wasteful process – creating a lot of food they won’t use. but I would be interested in seeing a link for that.

      Reply
  9. Thanks for the discussion on whether humus exists. While the evidence is strong that humic and fulvic acids do not exist in nature and are created in the lab, the existence of the starting material, humus, from which humic and fulvic acids are obtained by alkali treatment, remains unshaken.

    Question: Is the black colour of terra preta due to carbon (bichar) or to humus derived from carbon?

    If biochar is mixed into garden soil for a few years and then treated with strong alkali, would it yield humic and fulvic acids? If it does, that would indicate that biochar changes into humus.

    Reply
    • I am not clear about why the soil looks black. I saw a recent report that suggests a lot of it is carbon from previous fires. Adding compost to lighter colored soil does darken the color. The color is probably a combination of things.

      My understanding is that biochar is extremely stable carbon. After a few years in the garden it will still be biochar. Treatment with strong alkali won’t change it.

      Reply
    • I’ve been thinking about that bio char and humate comparison/similarities as well. In past posts I’ve mentioned how bio char is the new buzz word in the industry and how it’s being marketed with little if any peer reviewed data as a the new silver bullet. Water savings is the biggest claim being made and in my mind an easy one to disprove. Water retention is not water savings but that’s another topic. Humates and fulvic acids are also being marketed with undocumented claims. Go into any organic nursery/garden center or hydroponic store and see all the many products of fulvic acid, compost tea, humate ect all packaged with fancy labels and wow do the stores and salesman religiously support them and the claims. Makes me laugh. I also or at least try to point out that it’s the fertilizer charge included with the B1 or Fulvic Acid product as examples that show any plant response and it’s not a result of the B1 or Fulvic Acid. Myself and company are very involved with construction and maintenance of golf, sport and landscapes. I would love to start to see legit soil scientist or equal start to get way more involved with landscape architecture associations. If you ever get a chance look at some of the so called educational sessions that are offered at landscape architect trade shows or equal. Most of it is fringe science and products like compost teas, B1 and other feel good materials are discussed as tried and true products. I would like to see university professors involved with these groups way more than they currently are cause in my mind landscape architecture us where a lot of misinformation begins. I’m working on a huge project for the San Diego Zoo. The specs are ridiculous and will end up costing the Zoo literally $100,000.00 thousands more just because of some feel good products the soils consultant they hired choose to use. Oh by the way their soils consultant doesn’t even have a degree in soils or horticulture but only in Landscape Architecture. What a crazy industry we have.

      Reply
      • I think it’s a stretch to categorize compost tea as”fringe science” . Properly applied and brewed tea is known to effectively innoculate soil with desirable biology.

        Biochar is often ashy and consequently pH raising. It’s important to respect that effect when incorporating into your garden.

        Reply
        • Compost tea is NOT “known to effectively innoculate soil with desirable biology”.

          The science actually does not show any consistent results from compost tea, and there is little evidence that adding microbes to soil serves any real purpose except in some rare cases – certainly not in gardening.

          Reply
          • http://www.hindawi.com/journals/bmri/2013/863240/
            http://npj.uwpress.org/content/4/2/143.refs
            http://www.nature.com/articles/nplants2016107?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+nplants%2Frss%2Fcurrent+%28Nature+Plants%29&utm_content=Google+Feedfetcher

            Actually you’re mistaken (and bombastic). The most basic academic survey of biological soil inoculation will show loads of citations in support of the practice. If you know any professional gardeners who grow high value, organic crops run your “certainly not in gardening” ‘knowledge’ by them.

            From pumpkin farmers to golf course superintendents to MMJ growers bacterial and mycorrhizal inoculations are very often considered best practice. The outcomes are well supported anecdotally (see Acres magazine) and by academic citation(see above).

          • Since you did not say exactly what you are disagreeing with, I can only guess that it was my last comment: “Compost tea is NOT “known to effectively innoculate soil with desirable biology”. ”

            Your reference 1: Does not seem to deal with compost tea, but in any case it says in the Abstract “The extent of the inoculation impact on the subsequent crops in relation to the buffering capacity of the plant-soil-biota is still not well documented and should be the focus of future research.” This supports my position that there is not yet any scientific proof.

            Your reference 2: This also does not deal with compost tea. But it says “Roots ….. were more rapidly colonized by arbuscular mycorrhizal fungi (AMF) when grown in plots containing commercial or naturally occurring AMF inoculum, but after 68 wk plants growing in non-inoculated plots had similar colonization and biomass production.” So natural mycorrhizal fungi in the soil worked just as well as commercial products. You don’t need compost tea – which by the way is not a good source of mycorrhizal fungi.

            Your reference 3: deals with ecosystem restoration which is not the condition found in most gardens. I don’t see how this applies to gardening. In my comment I did say that compost tea may be useful in unusual situations.

            Finally you say ” The outcomes are well supported anecdotally (see Acres magazine) and by academic citation(see above).” Anecdotal evidence is not evidence of anything. Lots of people believe things that are not true. As far as the academic citations you presented – none contradict my comment.

          • I think the whole ‘compost tea’ hype is coming from the cannabis industry, which got it from that one scientist that wrote ‘The Soil Food Web’ book. The scientist used it on fields that have had their natural microbes destroyed and the cannabis industry uses it in pots with potting mixes that have very little soil microbes to begin with. So ofc in those 2 cases it will help, but I dont think it will do much in healthy natural soils in nature.

          • Start with facts.

            1) Dr. Ingham promoted the Soil Food Web concept and promotes the use of compost tea. As far as I know she does not promote the idea for cannabis.
            2) Cannabis growers may have adopted compost tea – they believe in a lot of nonsense.
            3) “fields that have had their natural microbes destroyed” – no such thing. Current agricultural fields have lots of microbes. They have changed a bit, and there may be fewer, but the idea that they have been destroyed is not true.

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