humus c'est la dernière phase d'évolution de la M.O

I agree.

Hello Mr. Pospelov,

I think SOM and humus can be used synonymously. However, this strongly depends on the used definition.

I can recommend the following article:

Article Advances in Understanding the Molecular Structure of Soil Or...

Further the progress in SOM research during the last centuries is elaborately described in :

Article Advances in Molecular Approaches for Understanding Soil Orga...

Dear Dennis Melzer, many thanks for the response and links to excellent articles. I hope to find answers to my questions in them. As I understand it, you are engaged in soil research, I wish you success in your studies. It is difficult to draw a line between SOM and humus when we study plant residues. So I'm looking for the right understanding and methodology.

SOM and humus are distinctly different. SOM includes all fractions of organic material in it’s multitude of stages of degradation, whereas humus is only the humic substances present at the end of the biological degradation of organic matter.

SOM represents the organic constituents in the soil, including undecayed plant and animal tissues,their partial decomposition products, and the soil biomass. SOM therefore includes non-humic components such as sugars and fats etc.

For more details on the subject please see attached files:

Dear Dr. Alhayany,

Thank you for your reply, comments and information sent. I completely agree with you in understanding the nature of humus and its origin. At the same time for me, the problem is correctly to estimate the SOM. If there are clear methods of evaluation for humus, which are fairly simple to perform, then we can not find good methods for estimating the SOM. Wish you all the best.

Definitely, SOM and humus are distinctly different.

SOM includes all fractions of organic material in it’s multitude of stages of degradation, whereas humus is the most stable form of organic matter that does not undergo any biological decomposition

Humus consists of humic substances that includes humic acid, fulvic acid and humin.

There is actually an intense discussion in SOM research, if SOM consists out of humic acids, fulvic acids and humins. Despite large scientific effort and improved analytic possibilities, it was not succeeded to evidence these humic substances in natural soil systems, so far. Thus, the actual existence (and the old humus paradigm) got more and more questioned during the last years. Recent papers acknowledge the origin of humic substances therefor as an artifact of alkaline extraction.

As stated above, this strongly depends on the applied definition. I would distinguish fresh organic matter (e.g litter) from SOM which are microbial processed organic compounds. I would further distinguish SOM into different fractions such as i) particulate organic matter (POM), ii) dissolved organic matter (DOM), iii) microbial biomass, iv) microbial necromass and v) mineral associated organic matter (MAOM). Each of these fractions can be estimated analytically.

This paper describes the "old" and "new" paradigm of SOM research:

https://www.nature.com/articles/nature16069

Dear Dr. Gaind,

Thank you for your participation in the discussion.

Daer Mr. Melzer,

Thank you for participating in the discussion and a link to an excellent article. Your opinion is very interesting and has the right to further development. Since the emergence of the science of soil and the study of the process of soil formation, the question of humus and organic matter constantly attracts the attention of scientists. And despite modern analytical methods, there is as yet no clear-cut assessment and understanding of the process. In your approach, the possibility of an analytical evaluation of each part of organic matter, including microbial biomass and plant residues of varying degrees of decomposition, is very attractive.

Interesting discussion and good/latest references on soil organic matter and humus. Professor M.Schnitzer,a famous worker on soil organic matter and its characterization, based on an interlaboratory collaborative study, published a simple (in 3 pages ) procedure to characterize the soil organic matter and the humic fractions Viz.,humic acid and fulvic acid and their characteristics.

A procedure for the characterization of soil organic matter. Schnitzer,M., Lowe,L.E. Dormaar, J.F. and Martel,Y.!981.Can.J.Soil Sci.61:517-519 (August 1981). A pdf is available from www.nrcrresearchpress.com

Another simple and practical procedure to determine humic matter is available in the following publication.

Colorimetric determination of humic matter with 0.2N NaOH extraction by Tucker, M.R. In: Reference Soil and Media Diagnostics Procedures for the Souther Region of the United States by Donohue,S.J. (Ed.). Southern Cooperative Series Bull.no.374 (1992) Virginia Agricultural Experimental Station, Virginia Polytechnic Institute & State University .Publication available online.

SOM is a microbial demposed matter whereas humus is a part of SOM which known as a lingnin protein complex.

Dear colleague, Dharmendra Gaur!

Thank you for your reply, I agree with your opinion of the main role of microorganisms in the depletion of plant remains and the formation of humus in the future

Dear Dr. Annangi Subba Rao!

Thank you for the informative answer and support of our discussion. I really appreciate your participation. I have carefully studied the methodological approaches that are set forth in the scientific papers cited by you. It seems to me that they are more concerned with the evaluation of humus and its constituents. To do this, use either alkali or a strong oxidizer. Nothing fundamentally new is proposed for quantitative analysis.

In turn, I have found methodological approaches, which, I think, are more suitable for assessing organic matter in the understanding of plant, microbial and animal remains. Perhaps someone knows more about this?

If SOM includes all fractions of organic material in it’s multitude of stages of degradation as many indicated here, then this organic, carbon-rich material is still chemically unstable and can be toxic to plants and inhibit their growth. On the other hand, humus in its various forms (e.g.: humin, fulvic acid, himic acid) is the stable form of organic matter and thus viable and effective in promoting plants growth and development.

Dear Dr. Borsari,

Thank you for participating in the discussion. Your opinion is very interesting from the point of view of the allocation of plant compounds to various compounds that can both stimulate and inhibit growing plants. Here you need to remember about allelopathy. This issue can be very important for organic farming, when using plant residues, siderates, organic fertilizers to compensate for the mineralization of humus and nutrients.

I agree with Bruno

Thank you Mr. Annangi Subba Rao for your discussion.

However, does the humic content affected by soil type when analysing?

Humic substances (HS) from environmental compartments can strongly differ in their chemical and physical characteristics, as a result of the diversified humification conditions. In soils, the structure and composition of HS seem to be influenced, among other parameters, by parent material, soil pH, vegetation, soil management system and cultivation1,2,3. Also the soil type, including its mineralogy, which in turn, is related to soil age and climate, can affect the quality of HS.

For more details ,please look at pending file:

Soil organic matter includes whole forms of organic molecules from living beings, which finally are free or still forming organomineral complexes, mainly comes from decomposition processes of living beings debris, roots exudation and the humification process. While humified organic matter comprises the most stable (more recalcitrant) and complex form of organic matter, generated from humic precursors (formed by partial decomposition of organicdebris) through polymerization and condensation processes; the humic matter is of greater importance for the formation of the complex whit clays and for the formation of soil aggregates, besides exhibit certain bioactivity on the plants (stimulates root development and promote metabolism - like auxin effect), while the other forms of organic matter (less stable) are more important as a source of carbon, energy and maintains the soil microbial metabolism.

Organic matter must pass several steps to become humus

The difference in the ratio of degradation and the state of the chemical elements