The term "humification" in Russian literature has a double meaning: firstly, it is the accumulation of organic matter in the soil, and secondly, - the content of organic matter in the soil. Usually the term "humid" is applied to the climate characteristics. It means - wet climate, that is characterized by «wet out» type of the soil water regime.

Dear Philippe,

I fully agree with you, we should move the field forward by re-defining what is humus, humified molecules and humification process instead of put into question the use of a widely used terminology. Especially because their paper did not demonstrate that humification proccess do not exist: e.g. humification can occur in soil by complexing dissolved organic molecules with metals. This process, imo, can imply humification and as such the formation of more complex humic substances.

Soil science is a very young discipline because till present days there is not a good theoretical base (foundations) for it. Without the foundations and theoretical systematization of knowledge in soil science (much deeper than today), this duscussion has no sense/ meaning.

I think that only theoretical soil science can show, for example, whether both directions (defined by Prof. A. Piccolo and Prof. Lehmann and Prof. Kleber) are rights at the same time and reflect the different sites and different fragments of soil organic matter.

However, there is a good direction in soil science developed in Russia and USA. Also, there is International Humic Substances Society IHSS. It will be better  to direct  this question to IHSS.

I have looked through  presented by Prof, Lehmann and Prof. Kleber in Internet, and I have found that nature of soil organic matter is not contentious but it is not sufficiently investigated.

I agree with your suggestion, Philippe. Talking with farmers is already confusing when the wordings humus, organic matter, and organic carbon, are used (including on the different analytical results they receive). Simply dropping these words will not improve the problem. It is also a difficulty with urban plantations: people think that mixing up compost and minerals makes a soil (or vegetable mould) and compost is "organic matter". This is a daily, and important, issue we face. We always have to recall what we mean with SOC or OM, and humus is often useful for that. The wording is also important when teaching, to future agronomists, civil engineers etc.,  easy/ good equivalents should be available in the national languages. Humus in German is vegetable mould, like it was in the past in French. We, soil scientists and soil science teachers, should be on the same line to help solving this difficulty.

I am probably not in the position to give direction or advise here. I only want to add that my general concern about using the word humification in this context is that it normally describes a break down process, which then makes humus a break down product. However, some soil organic matter will be formed or produced within the soil rather than the result of a degradation process. An interesting recent example of this are the bacterial graveyards that Kästner and coworkers have suggested as a significant part of the SOM.

See for example:

https://www.researchgate.net/publication/225565181_SOM_Genesis_Microbial_Biomass_as_a_Significant_Source

https://www.researchgate.net/publication/235625703_Microbial_cell-envelope_fragments_and_the_formation_of_soil_organic_matter_A_case_study_from_a_glacier_forefield

Article SOM Genesis: Microbial Biomass as a Significant Source

Article Microbial cell-envelope fragments and the formation of soil ...

“Death” is also relatively abstract as term and not enough scientific; even worse: dead matter becomes...“humus”!? 

And “food”, what’s “food”? “Food”, “digestion”, “metabolism”... just inside, just now… 

“Force of gravity”… to be banned until detection of “gravitons” ? And yet, it works … 

(“Si je doute, je pense, et si je pense, je suis” – Descartes, 1637) 

;-))

Dear Philippe, I agree with your suggestion not to drop the tem humus but to define it. Personally I would be sad to reject the term humus, which has the same origin than homo, just like Adam refers to dirt or clay. In both cases etymology shows the existential links between soil and mankind.

A rose is a rose and humus is humus. No matter what they are called they smell just as sweet to us. 

The term Humus refers to capacity to relate with moisture sharing the greek root HUM which is shared with humidity.

It is a good term that many have related to  and those that use it  have a good understanding of.. Humified substance is capable of being moist soft and wet optimally useful for us.

If we destroy a term by not using it we change focus intentionally or unintentionally. Ask a German what Gemutlichkeit means and in English there is not a ready translation but for the people that use it they know it intimately and exactly. It is the use of words that give them power. I like the word Gemutlichkeit also.

Whether we talk about soil Carbon organic matter or Humus they all are confused. Why? Because these do not refer to a monolithic substance at all but  they influence some many properties. They are a complement of components fractions. While they certainly not just the capacity to hold and transfer water but many other aspects and they are not a single component either.

While there is power in simplification there is also power in the fractions. All these are basically a mixture of fractions and components. They are dynamic and not static having some difficult characteristic that flux and change. This is why they are hard to understand with finality by destructive analysis and simplification as the sole strategy.

These substances seem to morph and while not being capable of reproduction per se they certainly have some dynamic reactions.

When simplification is the goal the ghost in the whole can be lost. In the case of Humus it is definitely more than the sum of its parts. Simplification does not capture its nature and potential and holistic rather that simplified approaches are probably better suited.  Nothing wrong with using both but do throw any away.

Humus is a good term which should be retained in our scientific literature.

Correctly, called of soil organic matter, which are not subjected to the processes of humification and humus formation  - humus?

I think, that this question has an answer for a long time (about 50 years). This is evidenced by the presentation that are used in the educational process (see File).

It should be noted, that the this issue have been the subject of a special discussion at the VIII International Congress of Soil Science (1964). Flaig W (BRD) made a detailed overview of existing terminology. However, there was not adopted a common nomenclature. Suffice it to say , that M. Kononova (USSR) proposed to divide the concept of "humus" and "organic matter".

F. Duchafour also considered it necessary to distinguish the concept of "humus" and "soil organic matter".

I hope this will be helpful to our discussion

Friends,

One should change terminology only if there is a good reason for it. I see no reason to switch from humus to SOM, simply because each term has its place in the scientific jargon. using the term "humus" implies organic matter that underwent stabilization (i.e., "humification") to become the degradation-resistant organic material the origin of which is not identifiable any longer and the composition and structure of which are not precisely known to date. SOM is a more diffuse term the use of which depends on the user. Wikipedia defines it as "Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesized by soil organisms." So lets leave things as they are. 

                                    Everything flows, everything changes...

                      (Heraclitus of Ephesus, approx. 554 - 483 BC)

In the soil can be up to 30-50% of “fresh” organic matter (plant mortmass, microbial mass, etc.), which is rapidly mineralized (even during the growing season). This is the main substrate of microbial activity in the soil. In this regard, there is no need to make this “fresh” organic material was converted to humus, which is practically inaccessible to the microorganisms.  It is  of the organic “skeleton” of  soil. It forms resistant organo-mineral structure. Thanks to these structures, being formed persistent biomineral body such as soil. Therefore, the soil contains  30-50% of labile organic matter - a functional pool and about the same humus - structure pool. In this connection, may not all soil organic matter called humus . If you do not differentiate on labile organic matter pool (fresh organic matter) and stable pool (humus), if you need to turn the history of soil science at 50-100 years ago. For what?

I have not gone through the article on humus being discussed but the discussion is interesting.As I understand  the humus has history of over 300 years.Several theories have come and gone but humus remained with changing new perspectives.I understand,agree and appreciate the sentiments and views of Drs .Augusto,Jean-Thomas,Hepperly,Christian and Mingelgrin .Figure. 2 in the following review paper provides an account of evolution of the soil organic matter concepts over the past 300 years.Historical evolution of soil organic matter concepts and their relationship with the soil fertility and sustainability of cropping systems by Manlay,R.J.,Christian,F,and Swift,M.J. Agriculture Ecosystem&Environment 119(2007)217-233 Available online at www.sciencedirect.com

 Dear colleagues,I have just gone through the presentation of Drs Lehmann and Kleber mentioned by Dr.Olga.I understand that  with all the techniques we have ,we failed to characterize the humus.Nobody can dispute the functions attributed to humus.Nobody  has said it is permanent in soil.So for nobody proposed any alternative model except for suggestion for a 'continuum' model.For every thing there should be beginning and ending Our starting point is fresh organic material added and our end product is humus,may not be a single homogeneous product(like big organic molecule)..One can not make humus dynamic and at the same time get benefits of CEC,aggregation ,structure ,water and nutrient holding and release.It shelters microorganisms when there is no sufficient food and water and maintains their minimum population,until they get fresh lot of food and water.Even many of our pools or fraction schemes  are fictions or method based As I understand so for there is general agreement on organic pools and fractions in soil.I need not comment on models based on those pools and conclusions drawn.Where all the soil  organic carbon is sequestered?In which form and how long it will survive?Can we call temporary and changing pool as sequestered carbon.?Whatever tools and techniques we may use ,we should not forget the existence of  a stable(not permanent) and,passive pool of carbon which we can call humus and its long term ecosystem services for the mankind/ humankind(dispute of terms).

As long as there are no really  new insights into the complex formation processes and structures of humus, the old terminology seems still adequate to me!

I think that the point is not the term but the piece of reality this word refers to. If different people do not have the same idea about humus, this indicates that there is a serious problem. It seems that the problem (how to define humus or even does humus exist?) is not new, having been at the centre of many discussions in soil science, agricultural science and soil chemistry. Now we know that fresh organic matter is submitted in the soil to a variety of physical and chemical processes, by which it is either lost to the soil (mineralization) or kept as a more or less stable dark substance (humification) in which it is terribly difficult to isolate molecules, at least as chemists like to do, i.e. by using extractives. We know that the nature of these molecules varies according to the method used to extract them from the soil, hence the discredit put on this terrible enigma. The reason is that chemists are unable to consider the world as other than an assemblage of molecular units, which it is not. Johannes Lehmann is a chemist, don’t forget it. He was trained and worked with Pr. Zech in Bayreuth in his famous laboratory of soil chemistry before flying to the USA once he discovered the charcoal origin of Amazonian Dark Earths. But what is humus for a biologist, not a chemist? Humus is neither a molecule nor a series of molecules, but a stage in the transformation of organic matter produced by plants, animals and microbes. When examining the soil with a microscope, without any extraction method (just by preserving a small volume of soil in alcohol), it is easy to discern a succession of stages from easily recognizable tissues and cells to pieces of them once they have been eaten by animals or transformed by microbial processes. To this must be added the synthesis of new organic matter by soil organisms (animals, microbes), their bodies being added to the soil organic matter transformed from plant leaf and root litter, wood and bark. What is humus in that variegated landscape? If we increase the magnification from the naked eye to the dissecting microscope then to the light microscope then to the transmission or scanning microscope, this dark molecular cloud reveals itself as an assemblage of pieces of living or dead organisms. If there is a stage beyond which nothing is still recognizable, then this stage lies well beyond what is considered as “humus” or “humified organic matter by chemists. Read (among others):

https://www.researchgate.net/publication/44180228

https://www.researchgate.net/publication/46312511

https://www.researchgate.net/publication/240321172

In this context, are we still speaking of “humus”? The answer is yes, because discarding a term does not discard the piece of reality which is hidden in it. Even though humus is the despair of soil chemists it gives to the soil a lot of properties which can be measured and reproduced experimentally and it can be used for agronomic purposes: humus helps the soil to hold moisture and nutrients, even in the absence of clay particles (a richness for tropical soils), it protects soil from erosion (because of many bonds with minerals and metal oxides), its darkness increases temperature, polyvalent cations protect it from mineralization, among many other features. Despite the opinion by Johannes Lehmann, humus is not in the dark…

Technical Report The soil under the microscope: the optical examination of a ...

Article Humus form dynamics during the sylvogenetic cycle in a mount...

Article Alimentary studies on the Collembolan Paratullbergia callipy...

 Dr.Jean-Francois,I am very impressed by your illuminating and factual answer.Humus may be a unifying concept but is diverse and distinct under different agroeco and forest systems.I like your poster on humus systems.You have nicely summarized humus or humified organic matter functions in your last paragraph.The humus functions may not be same everywhere but may differ in different ecologies but contributing to ecosystem services every where.

Some comments:

Each term/ word, which we use in science, implies a model of the objective world. The term “humus” arose in soil science to model/ characterize the complex organic matter of soil together with soil microorganisms and the processes in SOM and the soil environment.

Till present days, soil chemistry tries to tackle a chemical model to characterize the soil environment and the processes in the soil environment from the chemical view point but the continuous completed approach/ model was not yet found. It means that at the present, we can’t give ‘a more consistent, rigorous definition of the terminology, which corresponds better to the "new view" on SOM’. This all means a lack of investigations in different scientific planes.

One small example: how can the soil chemistry to explain a property of humic acids to decrease the entropy of some soil volume isolated from the bulk under specific conditions.

Humic substances are fantastic substances. They set the phase space/ nano cosmos where the uncertainty principle of Heisenberg becomes inoperative, whereas the condensed matter only begins to come into being.

In my works, I try to understand humic substances from physical and physicochemical view points, and it helped me to reveal some interesting phenomena in the soil environment connected with hydrodynamic instability and due to quantum properties of some humic substances.

 Dr.Olga,I find two two interesting points in your comments.Your last paragraph is  very informative.The main point is whether we have not properly characterized humus /humic substances or not?What is the' new view /views of organic matter 'which can not be explained with the present concept of humus and humus formation processes.Which components of present day organic matter concept/concepts are better explaining  the new role of organic matter ,compared to humus/humic substances?

                             Everything flows, everything changes...

                      (Heraclitus of Ephesus, approx. 554 - 483 BC)

Dear colleagues !

In the short term, fate of “humus” awaits the fate of “phlogiston”

Despite the fact, that many scientists, especially old, it is hard to part with the traditional concept. It is in the history of science knows things. For example, the long struggle fierce famous chemists of the essence of the process of combustion (oxidation). Since “humification” is also an oxidizing process, think of the phlogiston. The hypothesis of “phlogiston” was the first theory in chemistry and allowed to summarizea a variety of reactions. It was a notable step in the establishment of chemistry as a science. In the 1770s phlogiston theory was disproved thanks to the work of Antoine Lavoisier, after which it was replaced by another – the oxygen theory of combustion.

Although the evidence Lavoisier were absolutely clear, his ideas met with strong resistance among some scientists. One of these was Richard Kirwan, who long time was one of the most staunch supporters of the phlogiston theory, and even after the work of Lavoisier,  believed that "inflammable air"  is a pure phlogiston.  In 1787 he published "An Essay on phlogiston and Constitution acids ", which came out against the main provisions of the oxygen theory of Lavoisier. This work of  Kirwan became widely known thanks to the French translation by wife of Lavoisier, Anna Maria.  A new chemistry (without of phlogiston) Kirwan  accepted only in 1792!!!  He wrote K. Berthollet following lines: "After a decade of effort, I laid down their arms and leaved the phlogiston. I see now, it is clear, that there is no reliable of experience, that would prove the formation of "fixed by air" from hydrogen (phlogiston) and oxygen, and under these circumstances it is impossible to continue to consider fair flogiston system"

From well-known  scientists of that time,  the longest remained faithful to the theory of phlogiston was George Priestley. He, until his death in 1803,  zealously advocated in its defense, despite the opening of the era of the chemical revolution, completely refutes this theory. According to Cuvier, "he undismayed and not retreating, seen as the most skilled fighters the old theory over to the side of its enemies. And when Kirwan after all changed phlogiston, Priestley was left alone on the battlefield and sent a new challenge to their opponents in the memoir, addressed them to the first French chemist. "

It took more than 200 years ... and despite the fact, that Antoine Lavoisier and George Priestley differently seen combustion process, first and second steel Geniuses of Science.

But, the term "phlogiston" is not currently used in scientific works, except for works on the history of science.

This is the essence of Science!!!

The question of using or not using these words in the discussion of soil organic matter is a matter of "hegemony." Here we are seeing proponents against these terms trying to dethrone a conventional hegemony of those words relative to soil organic matter. For me, it doesn't matter as long as the soil is the center of my focus. 

 Dr.Jenkins,rightly said.All the elements in periodic table were there in nature even before their discovery by our eminent scientists. Similarly soil organic matter was there in nature and performing its functions in soil. even before coining the term humus.Like our life stages like childhood,young,middle and old ages ,soil organic matter has stages and functions in each stage.As per the current understanding we believe in active or labileSOM ,slow or intermediate SOM  and recalcitrant,passive,stable  SOM .Some times a little overlap of stages may also occur in different environments.Functions at different stages will also be different.Every stage has its unique role to play.There is no harm if we call the third stage as humus or by some other very elite name.

I think we have to concentrate more on slow and passive pools of SOM as much of our soil organic nitrogen(50% ) organic phosphorus(30-70%) and organic sulphur (I do not know exact percentage) are not properly characterized.  A lot needs to be done to understand their nature ,chemistry and role in agriculture ,ecosystem and environment.

Dear colleagues I could find two good reference on humus/humic substances structure as revealed by new techniques.

Molecular structure in soil humic substances:The new view. Sutton,R.and Sposito,G .Environ.Sci.Technol.,2005,39(23),pp 9009-9015.

Aggregation and disaggregation of humic supramolecular assemblies by NMR diffusion ordered spectroscopy(DOSY-NMR). Smejkalova,D. and Piccolo,A.  Environ .Sci.Technol.,2008,42(3),699-706.

Dear colleagues I could find two good reference on humus/humic substances structure as revealed by new techniques.

Molecular structure in soil humic substances:The new view. Sutton,R.and Sposito,G .Environ.Sci.Technol.,2005,39(23),pp 9009-9015.

Aggregation and disaggregation of humic supramolecular assemblies by NMR diffusion ordered spectroscopy(DOSY-NMR). Smejkalova,D. and Piccolo,A.  Environ .Sci.Technol.,2008,42(3),699-706.

But both papers give no substantial leads to new definitions, dear Dr. Rao!

Dr.Schnug,I am  talking of the structure of humic substances as revealed by new techniques,not new new definitions.As I understand, the humus chemistry, physics, microbiology even physiology(from plant nutrition point of view) are like ocean.We are in shallow waters  with our pools,fractions and models.As mentioned by me earlier we have to study the core of humus withe all its constituents,C,N,P  and S .Even the  four elements differ in their decomposition and mineraliztion patterns and requirements for the two processes.Can the present day models capture all the intricacies of chemical physical, biological and biochemical processes going on in soil organic matter?

I also think that the problem is not the terms humus or humification themselves. The problems with these terms are:

- the unprecise way they are too often used, to describe the product of a transformation which is not really characterized. A better definition would thus be useful, as proposed by Philippe

- the uncorrect use derived from these terms some decades ago by soil chemists: humic acid, humic substances, now suspected to be artefacts of the chemical extractions from which they derive, were considered as part of humus, leading to the suspicious consideration of the term "humus" itself. New methods to describe the formation and properties of humus are thus essential. And chemistry must not be banned (I am a chemist!) but more realistic chemical methods must be invented. Molecules and their association are important building blocks of humus, even if they cannot explain all its properties.

Very good points by Dr.(Ms).Marie-France.Two points raised are important-new methods to describe the formation and properties of humus are essential and second molecules and their association are important building blocks of humus.

Soil chemists and  fertility scientists including me always relied on chemical extraction procedures in soil testing,fractionation of nutrients like carbon,nitrogen,phosphorus and sulphur (even micronutients).Though earlier studies focused on extraction procedure,polymeric structures with high molecular weights,the current studies are  on supra/ macromolecular structures build on monomeric units .Like a protein structure built from primary ,secondary,tertiary structures to Quaternary structure, one day our humus may also get a Quaternary three dimensional structure explaining many properties,though more complex than protein.

One of the major problems in communicating in the field of humic substances is the lack of precise definitions for unambiguosly specifying the various fractions. Unfortunately, the terminology is not used in a consistent manner. The term humus is used by some soil scientists synonymously with soil organic matter, that is to denote all organic material in the soil, including humic substances. Contemporary, the term humus is frequently used to represent only the humic substances.

The term SOM is generally used to represent the organic constituents in the soil,including undecayed plant and animal tissues, their partial decomposition products, and the soil biomass. Thus, this term includes:

It is likely that SOM contains most if not all of the organic compounds synthesized by living organisms.

 SOM is frequently said to consist of humic substances and nonhumic substances. Nonhumic substances are all those materials that can be placed in one of the categories of discrete compounds such as sugars, amino acids, fats and so on. Humic substances are the other, unidentifiable components. Even this apparently simple distinction, however, is not as clear cut as it might appear.

http://karnet.up.wroc.pl/~weber/def2.htm

Dr.Zenon,I appreciate your effort to explain the different terms connected  with soil organic matter.But I find two ambiguities in the attached literature.In the flow chart  initially the living organisms(Edaphon) and soil organic matter are grouped under organic compounds of soil.Organic compounds of soil may not appropriately accommodate the living organisms.Again the transformed product(humus) is subdivided into humic and non- humic .At least the humus in the bracket should be removed.The three groups of materials grouped under soil organic matter are o.k.But the undecomposed or partially decomposed plant or animal residues are not normally included in soil organic matter.As I understand the organic residues  should become  a part  of soil to be called soil organic matter.But because of new fraction schemes lot of ambiguity is created.It is a question whether to include the fresh,un-decomposed,recognizable or partially decomposed plant or animal residue as soil organic matter.

Dear  Annangi Subba Rao, 

Organic compounds of soil may not appropriately accommodate the living organisms…. Why? The soil, as we know, there is a “biomineral” body of Nature. In one kg of soil contains 500 billion bacteria, 10 billion actinomycetes,1 billion fungi, 0.5 billion microfauna. During the growing season, in the soil is replaced about 10 generations of microorganisms.  The major chemical elements, prevailing in the cells of the microorganisms are Carbon, Oxygen, Hydrogen and Nitrogen. They form the basis of organic substances, so called organogenic elements (90 - 97% dry matter). Other elements are called ash, or mineral, they accounted for 3 - 10%. Most of them is Phosphorus.

It is understood, that in case determination of the organic matter of the soil, these microorganisms not removed !!!

Other Your comments will discuss later.

Regards

To say simply, organic compound is a small unit and living organism  is  a bigger unit ,both may be present in soil in large numbers.In that sense I have commented.

Here is another link:  FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS   Rome, 2005

The importance of soil organic matter. Key to drought-resistant soil and sustained food and production

P.15  Soil organic matter consists of a variety of components. These include, in varying proportions and many intermediate stages, an active organic fraction including microorganisms (10–40 percent), and resistant or stable organic matter (40–60 percent), also referred to as humus.

P 15. Forms and classification of soil organic matter have been described by Tate (1987) and Theng (1987). ….belowground organic matter consists of living soil fauna and microflora, partially decomposed plant and animal residues, and humic substances.

http://www.fao.org/docrep/009/a0100e/a0100e.pdf

Dr.Zenon ,I think there is some misunderstanding in use of terms.I never objected to include soil organisms/microorganisms under organic matter.I know very well that and I need no literature support.In the literature supplied  by you the soil organic matter and soil organisms were grouped under organic 'compounds'. My objection was for the use organic compounds,normally a smaller unit, for grouping  bigger units soil organic matter and soil organisms.Hope, I am clear in conveying my view.

Dear all,

Three years ago, right after the publication by Johannes Lehmann and Markus Kleber of their 2015 Nature paper on humus, I asked this question in RG... I thank you all for your input, which has been very interesting.

In spite of Lehmann and Kleber's suggestion to drop the terms of humus and humic substances, I notice from the literature that the terms continue to be used at the same rate... I guess, like many of you (and I) do, most of our colleagues consider that it is probably more fruitful to define old terms properly, rather than abandon them.

Incidentally, this was also, clearly, the point of view held by Waksman as early as 1936. As I read his amazing book on humus (to write a short paper on this whole debate about humus and humic substances) I realise that some of the things he wrote in his book 80 years ago, after reviewing in detail more than 1300 references (!!), are totally in line with what recent work, using advanced spectroscopic techniques, has rediscovered....

When my opinion piece about humus gets published, I will post a link to it here, to kind of close this discussion...

Thanks again to all of you for your thoughtful responses!

Philippe

Changing terminology does not affect substance. I totally agree with Philippe that a more rigorous definition of accepted terms is the right thing to do rather than sawing confusion by inventing new terms for old (even if better understood) entities.

Uri

You have to know how to use these Terms

Following.

Hello everyone,

Those who have followed this question over the last 2 years might be interested to know that Professor Michelle Wander (University of Illinois) and I have published an article dealing with humus, in which we address the question of terminology. You can find the abstract at this web site: https://www.frontiersin.org/articles/10.3389/fenvs.2019.00027/abstract. The full paper will be available in a few days (you can set up an alert). The bulk of the paper is on the structure of humid substances. I think that we are going to see a very lively debate on the topic in the next few months.

Best regards.

Philippe

Hello again...

As a follow-up to my last e-mail, the full version of the paper I mentioned then (in Frontiers) is now available for download (for free since the journal is in Open Access)... The web site is: https://www.frontiersin.org/articles/10.3389/fenvs.2019.00027/full

Best regards.

Philippe

Very interesting paper, merry go round soil organic matte/humusr research, worth reading.I request all soil scientists and soil microbiologists to read the article.Whenever new research project on soil organic matter is conceived and planned both soil scientist(s) and soil microbiologist(s) should be associated and should work together.Interdisciplinary work is needed, otherwise we will end with half truth/incomplete story.The physics,chemistry and microbiology of soil organic matter must be studied simultaneously with newer techniques to get new insights ,understand the full meaning and complete the story.

Hello everyone,

There's a recent special section in the Journal of Environmental Quality which should be of interest to everyone here. Here's the DOI to Henry Janzen's preface: doi:10.2134/jeq2019.01.0001c

And here the link to the full special section, incl. two viewpoint articles by Markus Kleber & Johannes Lehmann and Daniel C. Olk et al. and a commentary article by Satish C. B. Myneni: https://dl.sciencesocieties.org/publications/jeq/tocs/48/2#h1-SPECIAL%20SECTION:%20VIEWPOINTS%20ON%20THE%20FUTURE%20OF%20HUMIC%20SUBSTANCES%20RESEARCH

Enjoy the read!

Thank you, Carsten Simon, for references, which are definitely of great interest. One comment (in fact, much more:-)) regarding the minor issue in the paper by Kleber and Lehmann. It is in relation to considerations of solubility of organic components at high pH and relevance of highly exotermic solvation heats (shown in Table 1). To the best of my knowledge, the way of this reasoning is not correct. If comparing "solubility" of a non-ionized functional group/compound with that one ionized in solution, a proper cycle is applicable as following: 1) transfer of "group' to vacuum, 2) vacuum (gas phase) ionization (for ionized compound), 3) solvation/hydration of anion and proton (where, in fact, proton undergoes neutralization reaction with OH-). Therefore, the difference between acetic acid and acetate shown in Table 1 is not straighforwardly relevant, since it does not consider the endothermic heat of COOH ionization and exothermic hydration/neutralization of H+, too. In fact, most probably, the third factor is what makes the overall entahlpy change negative. However, more importantly, all the story with solvation heats is hardly relevant and not really needed since pH>pK increasing the speciation will immediately reduce, by definition, the solute chemical potential, thus assisting in increased solubility. This will happen also with endothermic solvation heats (but at pH>pK). I reiterate that it is a very minor issue ....

In my opinion, it is better to discuss the humic acid (non-dissolved at pH 1) and fulvic acids (dissolved). We are trying to make them more understandable using many perspectives. My research group is now trying to define and characterize them in a better way in soil DOM using EEM-PARAFAC modelling. This is directly linked with terrestrial humic-like substances in surface water and similar substances are also produced from phytoplankton (Mostofa et al. 2013). Therefore soil humic substances (humic and fulvic acids) and autochthonous humic-like substances of phytoplankton origin has a good linkage, which is better to understand many biogeochemical phenomena in that regards. Defining humic substances will provide us to understand many biogeochemical phenomena, not only in soil ecosystems, but also in water environemnts. Our first manuscript in soil humic substances is in the final stage, which will provide some useful information in that regards.

Reference:

Mostofa KMG, Liu CQ, Yoshioka T, Vione D, Zhang YL, Sakugawa H (2013) Fluorescent dissolved organic matter in natural waters. In: Mostofa KMG, Yoshioka T, Mottaleb MA, Vione D (Eds), Photobiogeochemistry of Organic Matter: Principles and Practices in Water Environments, Springer, Berlin Heidelberg, Chapter 6, pp 429-559

Humus is very likely derived from the condensation of the soil organic compounds that were dissolved at higher pH but deposited at low pH. May be we can refer them as the solubility of these organic compound are pH sensitive. So, if there is a pH gradient with high density, may be we can isolated them one molecular before another from very low pH to higher pH conditions, but they are only the part of the total organic compound in soil matrix.

It’s possible to assume that the humic substances exist in soil but they are not in that kind and in that quantity which is extracted by chemical fractionation after Tiurin’s method or IHSS. Moreover, having the same chemical composition they are very specific in 1) geometric form, 2) ratio between supramolecular and polymer structures and 3) other characteristics in different soil types. Currently, the practical procedures of humic substances extraction are far from perfection. The attempts to study their natural status in soil samples are rather descriptive by nature and should be scientifically grounding and interpreting with the required accuracy (Kogut. Semenov, 2014) 

In our opinion, the following Humus definition is more appropriate to the present eco-bio-physico-chemical concepts: “humus is a soil subsystem formed from the organic substances and compounds of plant, animal and microbial origin stabilized through the humification and non-humification pathways”. Humification is a (bio) chemical alteration of organic residues with the formation of humic substances, whereas the nonhumification stabilization is another process and phenomena which are capable to increase the stability of organic substances to biotic and abiotic effects without their transformation into humic substances. Humic substances is a biogenic, amorphous, heterogeneous, and chemically active continuum of biomolecules that is recalcitrant under natural conditions and is formed through random chemical transformations and physicochemical

interactions of diverse precursors with the formation of supramolecular

assemblies from different numbers of individual components of relatively

low molecular weight due to nonvalent interactions.

Semenov V.M., Kogur B.M. Soil Organic Matter. Moscow: GEOS, 2015. 233 p.

Dr.Semenov, good /interesting definition and description of the humus.

In this regard the recent essay by Dr. D.L.N. Rao (pdf attached) may throw more insight in to this wonderful subject area of soil research.

Methodology may have some problem, but until finding best one that can be used for their better understanding not only in the soils, but also they are contributing aquatic environments. Soil Scientists are needed more efforts to further progress. There are some recent articles that can be more understandable.

References:

Olk DC et al. (2019) Environmental and Agricultural Relevance of Humic Fractions Extracted by Alkali from Soils and Natural Waters. J. Environ. Qual. 48:217–232 (2019)

Baveye PC and Wander M (2019) The (Bio)Chemistry of Soil Humus and Humic Substances: Why Is the “New View” Still Considered Novel After More Than 80 Years? Front. Environ. Sci. 7:27. doi: 10.3389/fenvs.2019.00027

Baveye PC, Otten W, Kravchenko A, Balseiro-Romero M, Beckers É, Chalhoub M, Darnault C, Eickhorst T, Garnier P, Hapca S, Kiranyaz S, Monga O, Mueller CW, Nunan N, Pot V, Schlüter S, Schmidt H and Vogel H-J (2018) Emergent Properties of Microbial Activity in Heterogeneous Soil Microenvironments: Different Research Approaches Are Slowly Converging, Yet Major Challenges Remain. Front. Microbiol. 9:1929.

Nice explanation by Prof. SL Larson. Thank you.

Dear Steven, thank you for your interesting and helpful comment. Of course, in the whole you are right, but I would like to make two remarks. Firstly, in one of his articles, Brookes et al recall such a historical episode. At the final dinner of the International and British Society of Soil Science Meeting in 1983, held at the University of Reading, UK, the guest speaker, Professor Heinz Wolff, remarked that ‘It is not the requirement of a scientist to be right, but to stimulate others’. So, the scientist should prompt the true meaning of the terms and phenomena to the gardener so that he can correctly use the knowledge in practice. A gardener should also know that the terms “humus” and ‘SOM” are not synonymous.

Secondly, a comparison of humic acid and citric acid is apparently not correct. Citric acid has a known and constant composition, we know the ways of formation of citric acid, but we cannot say the same about humic acid, assuming that it is real in nature. It would be correct to call humic acid as an alkaline extract from the soil (sediments), which has those properties and qualities attributed to humic substances. Alkaline extraction is not contested by either chemists or soil scientists.

Semenov et al. Humification and Nonhumification Pathways of the Organic Matter Stabilization in Soil: A Review. Eurasian Soil Science. 2013. 46(4):355-368. DOI: 10.1134/S106422931304011X

One may not call humic acid a simple chemical but it is an entity which is complex in structure , have certain characteristics which are universal irrespective of source of extraction,does certain functions in soil which gives is a rare distinction and has even some plant growth stimulating properties.So humus assumes a separate place in soil -plant ecosystem and recognition characteristic of its own.

Dear Professor the humus is part of the soil or not, so should not be quoted term and color that humus may be part of organic matter, but a separate entity and has a role in the soil with sincere thanks and appreciation

Humus is the non-dissolved form of organic matter that is a part or fraction of soil that is approximately < 5% that varied depending on soil types. Humus can not separated due to its complex mixture with all other components, such as sands, clays, metals, etc. Colour of the soil depends on the presence and contents of metals and types of vegetation that have originated soil organic matter along with time and space when they were buried or formed.

I recommend the new article by Wells and Stretz. Article Supramolecular architectures of natural organic matter

Dear Waqas, humus is inherent only to the soil in contrast to humic substances that may be present in the soil (in the form of humus), water, atmosphere, sediment, manure.

Thank you

As we move away from bulk measurements and towards a resolved understanding of what comprises the dissolved or particulate organic matter pool in any system, we should I think move away from broad-brush terms which have no meaning at the molecular scale. Banning the term (rather like banning the ubiquitous, but erroneous 'nitrates' term) would be pointless. Rather we should be expecting more resolved terminology with more specific meaning, in any cutting edge research as we move the field forward.

An important contribution to the discussion on the name humic acids (HA), fulvic acids (FA) for a special group of natural nano-particles extracted from soils and natural waters is the paper:

Environmental and Agricultural Relevance of Humic Fractions Extracted by Alkali from Soils and Natural Waters

D. C. Olk,* P. R. Bloom, E. M. Perdue, D. M. McKnight, Y. Chen, A. Farenhorst, N. Senesi, Y.-P. Chin, P. Schmitt-Kopplin, N. Hertkorn, and M. Harir in J. Environ. Qual. 48:217–232 (2019) doi:10.2134/jeq2019.02.0041

This review first addresses specific conceptual concerns about humic fractions and then stresses that a large number of studies have shown that the extracted materials indicated as HUMIC FRACTIONS (HA, FA) are suitable for studying natural organic matter structure and function in field conditions. Therefore, the indications HA and FA are quite useful in practice and ave led to a better understanding of HA, FA physiochemical properties.

Dear Luuk,

It is very understandable that researchers who have spent a good deal of their career working with soil humic extracts or (as in the case of the first author of this paper you mention) are associated with a company that sells humic extracts to farmers, they would want to defend their use. But the real discussion hinges about what you mean when you write that "humc fractions are suitable..." Sure, they may be suitable for some things, and it is possible that, vaguely, their properties be correlated with those of the real soil organic matter they originate from, but is it not infinitely better to try to understand this soil organic matter directly, without extracting it, and possibly creating all kinds of artefacts? The same goes for the so-called "glomalin" we have been talking about so much in the last 20 years, and still know very little about... I think that we should stop blindly extracting things from soils to analyse them... (Don't get me started on all the extractions of DNA to characterise soil microbial populations)...

Dear Phillipe cs.,

One may have to accept that different philosophies exists with respect to investigating complex natural materials such as natural waters and soils: (1) those that study these materials empirical in their natural presence, and (2) those that separate a natural material in different components and then study these components. There will always remain debate about the pros and cons of these approaches. With highly complex systems generalization of empirical results is difficult and lots of information (often obtained by defining different subcomponents) is required to make (statistically sound) general conclusions. Separating a natural material in different components and studying the components, gives good information on the components, but to add-up this information to describe the properties of the natural material is still a difficult task because in the entire material the components may mutually interact and behave differently from the isolated materials. Therefore, both approaches will give us some answers, but also leave us with questions. The two types of philosophies will remain, are complementary and each approach has its own supporters. Why one is a supporter of philosophy (1) or (2) is a further question with many answers, but it is quite logical that one supports the choice made. Researchers of both types of philosophy will be happy to find support in literature for their work. The paper Environmental and Agricultural Relevance of Humic Fractions Extracted by Alkali from Soils and Natural Waters is written by supporters of philosophy (2) and provides arguments for studying humic fractions and their way of isolation.

Until finding a new approach on isolation of soil humic substances or soil organic matter, I agree with Prof. L. Koopal viewpoint. I strongly believed that very soon there will be developed a new approach that could deal with proper isolation of soil humic substances and explained effectively on respective soil biogeochemical consequences.

What are the current opportunities/ techniques available to study the intact ,original complex organic molecules or structures in soil, sediment or water with out employing any extraction procedures? As I understand extraction and isolation are common procedures to study biological or non-living systems for understanding their structure, composition , properties and functions .Can scanning the entities, with out disturbing their integrity, give complete information on the aspects mentioned above?

It is a common argument in favor of extraction methods (for both humid substances and microbial DNA) that there are no alternatives. But this is a vicious circle, since the more we work on extraction, the less time we spend on developing alternatives... But alternatives exist. As discussed in the recent paper Michelle Wander published on humus (https://www.frontiersin.org/articles/10.3389/fenvs.2019.00027/full), the very good work carried out by Dawit Solomon et al., using NEXAFS, is a great example of the use of techniques that allow us to study humid substances in situ, without extraction. This work needs to be pursued and extended.

Dr. Philippe , every body interested in the subject should read the conclusions of the article attached by you for better appreciation of the work on soil organic matter and future work on the aspects mentioned.

I suggest if the Scientific community wants to abandon the terms i.e. humus and humic substances, it should take a sufficient time to abandon these completely. I agree with Philippe's suggestions to redefine the terms properly so it will be clear to everyone who will do the related work in future. Since these terms have a strong imprint on our minds. So, its better to redefine the terms or find a better solution to address this problem.

Very good and interesting discussion

I need more clarification on this

it would be simply unacceptable not just for the discipline of soil science, but also for society at large, if we did not break the interdisciplinary barrier that has stood in our path so far. Understanding the dynamics of soil humic substances and natural organic matter is too crucial for us to avoid yet again taking the path not traveled.

Really very interesting.

And in the same paper, the authors write 'that soil organic matter is composed of inherently stable and chemically unique compounds'. Exactly for their uniqueness, those compounds ('associates', 'supramolecules', etc.) were allocated to a separate group called 'humus' and later 'humic' compounds. That is why I suggest that the Lehmann and Kleber's suggestion is baseless and rather rhetorical. Certainly, one can juggle with terminology, however, my opinion, these terms serve technically well to denote a group of specific natural compounds.

Soil humic substances are defined based on the fluorescence spectroscopy after their extracted from three characteristic soils under different extraction conditions. The link for this publication (Source URL:

https://authors.elsevier.com/a/1agIFB8ccoAKw). Hoping that debating on existence of soil humic substances will be resolved after this publication.

Very good contributions, I have a question about:

Fungi are capable of depolymerizing humic substances and is it possible for them to re-polymerize?

If you know any article to clear my doubts, I would appreciate it.

Dear Dr. Darlinson,

Fungi are not able to re-polymerize the same components. But they are able to get the mineralized end products (nutrients or CO2, DIC) from released humic substances for their growth. Thank you.

Dear Khan M. G. Mostofa, if I understand the action of fungi, but what I mean more is how and because humic substances have that ability to re-polymerize.

Thanks for the input.

Dear Darlinson,

You are wrong about the re-polymerization by humic substances. Humic substances does not re-polymerize, rather they are derived from complex states of microorganisms along with other inorganic components in soils. In water, autochthonous humic-like substances are derived from phytoplankton or algae. This is the authentic information from current understanding.

Dear Khan.

Thanks for the contribution, I need to go deeper into the area, but there is abundant research in this field and I find it difficult to understand the veracity of its conclusions, since we all have different points of view.

Philippe, I agree with you that it is "probably more fruitful to define old terms properly, rather than abandon them". I recently found a review that discusses some points that may be interesting on this issue. Here it is: Article Concepts and Misconceptions of Humic Substances as the Stabl...

Agree, there are many terms that need proper definitions, not only this one.

If there is no humus, which is the beginning of the soil, or "humification" which is the process of biological soil formation, then there is no soil either. Notice that the promoters of the discussion are chemists. Chemists shouldn't exist, because on closer inspection chemical reactions are purely physical processes. Chemists are physicists, eventually. So: away all the chemists, fired, because they don't exist.

On a more philosophical and theoretical note, I would like to add that all this knowledge about humus and humification during the last 200 years forms an important component of the history and culture of soil science. Terminology is useful to communicate in a language and it takes time to reflect about it, correct it and translate it so that it may mean the same in different languages. Therefore, I think that this knowledge should be conserved because without it we cannot move forward. Eventually, new a terminology will emerge with new paradigms and views about soils however, let's time take its course, without obliterating what has been learned, so far.

Thank you Bruno, this was my purpose, indeed, to look at the path of knowledge, beautiful especially when doubtful and uncertain, to be considered with respect even if it seems devoid of cutting logic. Because it resists investigation and opens up more easily to an artistic understanding of the act of existing.

So wowsers, this is making my head hurt - if its not humification than what is it?

Humification is a process of organic residues converting into humic substances. It is the real process. The formation of humus as a stable part of soil organic matter in size of

In 2018, a group of humus friends (nearly 200) published three HUMUSiCA Special Issues of the Applied Soil Ecology journal (https://www.journals.elsevier.com/applied-soil-ecology/special-issues). Focusing on humus instead of the chemical and physical aspects of the soil, these people changed the meaning of the concept of soil. With fundamental repercussions in agriculture and in natural sciences. A humus-free soil contains no life and exists only outside the critical zone. It's rock. A soil-with humus is alive; it is built by the living because they evolve with it. Do you want to see the primordial humus? Look for it in the genius Miller-Urey experiment. These Researchers showed how humus was born. The whole Universe may be nothing but Humus in evolution.

As I understand Humus, an entity present in soil, is basic to life in soil.It participates in longterm processes in soil.

lf some body desires to define the entity differently let him try. But he should be able to connect it with all the processes going on in the soil. All the soil reactions in which Humus participates needs to be reexamined and redefined with the newly defined entity, Unless the full story is not told with the new entity, the new entity can not replace the old one. Let us examine whatever shortcomings pointed out in the Humus concept and see whether there is need to define Humus differently to interpret all reactions and processes going on in soil.

Dear Annangi Subba Rao, you are right.

Humus is a soil manufactured by living organisms (mainly microorganisms, but also worms, arthropods, mammals, and plants), made of air, water, mineral matter and dead or alive organic matter. Commonly and mistakenly only the most organic and dark soil is called humus. It is actually difficult to separate the concepts of soil and humus. If we want to clarify, we can roughly distinguish the soil in three layers or groups of horizons [Humipedon: (O + A), Copedon (E + B) and Litopedon (C + R)], and make Humus correspond only to the Humipedon. In reality, humus is all the Earth's soil. At many scales, from microfilms to very deep pedons. There is no humus on the moon or on Mars, where soils have been described instead. Humus = soil inside a critical zone; Soil = soil inside and outside a critical zone. Critical zone = volume of the universe permanently inhabited by living organisms.

Nice to have your comments, ciaooo

Augusto Zanella Thank you for your interesting comments on inseparable relationship between soil and humus.

Humic sub (humus) the recombined pies of the SOM, more ever that natural polyfunctional material (biocoloids like natural nanomaterials) serve soil and aquatic ecosystem. The fraction of HS can structured soil and matter by means of hydrophbic-hydrophilic properties, depending on temperamental interactions (through intermolecular interactions of the state of water, exchange of low-molecular compounds) into an hierarchical structure within the structure of a complex system, forming from supramolecular associates (guest host) to macrocoloids and gels.

Of course....it would be irrational to ban the words humus, humic, or humification only because L&K do not understand what they are....ah, ah, ah, ah

I would like to thank all those who in recent months, have posted answers to my initial question. They keep the debate going, which is a good thing. Although I have to admit that, if I were starting my career in soil science, I am not sure that the extremely low level of intellectual exchange in general in our discipline (not just on humus, but on many other topics as well), would make me rethink whether this is a discipline in which I would want to spend the next 40 years. It has been 6 years since I posted the question, and 2 years since Michelle Wander and I published an article to try to answer it (Baveye, P. C., & Wander, M. (2019). The (bio) chemistry of soil humus and humic substances: Why is the “new view” still considered novel after more than 80 years?. Frontiers in Environmental Science, 7, 27.). Have we made any progress? In fact, since Alessandro Piccolo came up with his landmark articles 20 years ago, have we moved forward? It seems to me that the answer is a resounding "no"... That does not mean that we have to stop trying, of course. But I would strongly encourage the younger generation of soil researchers to think carefully about how they can change the navel-gazing culture of our discipline, so that real progress can be achieved. Right now, some people are very successful at publishing articles that attract lots of citations, but I don't think that much progress is made in the process... That needs to change! We need to start asking meaningful questions, about which we should have thoughtful debates, with the goal of coming up with definite resolution.

Dear Philippe

thanks for your further comment. You came out with the correct and timely consideration. There is little or no intellectual exchange in the realm of Soil Science Research. I stopped going to the World Soil Science Congresses several years ago because of the boring routine of the same old studies repeated over and over again only to give a tribune to the colleagues occupying positions in the IUSS Board! Nevertheless, we should ask ourselves why young scientists, who have not yet fallen prey of the societal politics, do not explore new areas of research and are not stimulated to do so. One first answer that comes to my mind is that they may lack the curiosity (or better the scientific background) to read reports from other fields, namely advanced hard-science papers in chemistry and biochemistry, which may open their mind to new techniques and understanding and try to apply them to Soil Science issues in order to broaden their horizons. You mentioned, I am grateful, my papers of 20 years ago which are still quite nicely cited today. However, few have taken notice of the mass of further research that my group has published on the charactrization of soil humus by the humeomics technique that we developed in last 10-15 years first on humic extracts and then directly on soils. By this approach we have almost completely mapped the molecular composition of soil humus, that we now call HUMEOME. Why these unprecedented results are given such insignificant attention? Indeed, it should be realized that such a detailed molecular knowledge of the soil Humeome should open up, to my view, research highways to figure out new technologies for the control of humus in soil, thereby increasing the soil capacity to nourish plants (including physiological studies devoted to build up structure-activity relationships between humus structure and its bioactivity) and control of environmental pollutants. We tried to do so by developing the use of biomimetic catalysts (again ideas stemming from actively perused contemporary hard-science literature) to polymerize the humeome in situ in soil and increase SOM accumulation and control of GHG emissions, as well as to fix organic components into the humic structure by covalent bondings and thus eliminate soil contamination. We enjoyed much these new research lines but it seems that we failed to stir attention to them. Too much strange for soil scientists? Not enough scientific background to appreciate them? This may be true considering the reached infimous level of chemistry and biochemistry understanding of Italian students of the AgricuItual sectors (not for their fault, however). I would be pleased to hear your comments. My best regards. Alessandro