Why Are Humic Substances Called Acids?

By Richard Lamar, PhD
Senior Director of Humic Research
Bio Huma Netics, Inc.

We are accustomed to seeing humic substances (humic and fulvic) in dry/granular form, and we tend to think of acids as liquids. So why are humic and fulvic substances called acids?All substances, solid AND liquid, have a chemical makeup. An acid is a chemical that can donate a proton (H+) to a water molecule (H2O, which would form H3O+) or to another chemical such as ammonia (NH3, which would form NH4+).

Organic acids are generally weak acids that do not completely dissociate (i.e., donate a proton) in water in the way that strong mineral acids do, such as in the case of hydrochloric acid (HCl). The most common organic acids are carboxylic acids, sulfonic acids, phenols and alcohols (Figure 1).

Organic acids can be aliphatic (structured as open chains rather than aromatic rings), such as acetic acid (Fig. 1A) or ethanol (Fig. 1E). Organic acids can also be aromatic (made up of ring structures, originally named so because of their fragrant properties), such as benzoic acid (Fig. 1B), benzene sulfonic acid (Fig. 1C) or phenol (Fig. 1D).

All of these structures can be found in humic and fulvic acids, sometimes all in the same molecule. For example, one humic acid or fulvic acid molecule might contain a benzoic acid, a phenol, an alcohol, and an aliphatic carboxylic acid (Figure 2). All of these functional groups can ionize (i.e., lose their H+ atoms and contribute to acidity) (Figure 3). The primary factor affecting ionization of organic acids is pH.

Figures 1–3.
Chemical structures found in organic acids

We will discuss the interrelationship of soil, pH, and humic substances in Humic Corner #4.

BHN Sponsors Online Course on Sustainable Organic Agriculture Production

To help increase awareness about sustainable agriculture production, Bio Huma Netics, Inc., (BHN) is sponsoring a FarmProgress course for Certified Crop Advisers (CCAs) and Pest Control Advisers (PCAs) in the United States and Canada.

This free online continuing education course, titled “Organic/Sustainable Agriculture Production -2022” aims to help working professionals learn about sustainable farming practices and pest management without the use of synthetic chemicals.

During the training, participants will learn about most common pests in organic/sustainable agricultural systems and current methods of controlling insect pests, weeds, and diseases in a range of organic crops grown in the United States.

The two-hour duration course is divided into ten sections and allows participants to complete it at their own pace.

Course Structure

Section 1: Introduction

Section 2: Organic Agriculture

Sustainable / Organic Management Options for Major Insects and Diseases of:

Section 3: Citrus

Section 4: Grapes

Section 5: Pome Fruit

Section 6: Blueberries and Strawberries

Section 7: Stone Fruit

Section 8: Nut Trees

Section 9: Vegetable Crops

Section 10: Forage Crops

“Pest management is an integral part of conventional and organic farming and requires adequate training. At times, managing pests in organic farming systems is much more challenging because of fewer options than in conventional production. By taking this course, participants can learn how to identify and combat pest infestation to minimize crop damage under organic cultural practices,” says Dr. Mojtaba Zaifnejad, Sr. Director of Field Research and Technical Services, BHN. In addition, this course provides a brief insight on how humic substances can benefit the health of soil and crops.

To enroll, or to learn more about the course, visit AgCEUOnline.

JoVE Video Journal Publication: Quantification of Humic and Fulvic Acids

Dr. Richard T. Lamar and Dr. Hiarhi Monda of our Humic Research Laboratory, with assistance from analytical chemist Ryan Fountain, have published a methodology video in the biochemistry section of the peer-reviewed online video journal, JoVE.

The video, Quantification of Humic and Fulvic Acids in Humate Ores, DOC, Humified Materials and Humic Substance-Containing Commercial Products, shows the step-by-step laboratory methodology (the New Standard Method) for gravimetric quantification of humic substances (e.g., humic and fulvic acids) on an ash-free basis, in dry and liquid materials from soft coals (i.e., oxidized and non-oxidized lignite and sub-bituminous coal), humate ores and shales, peats, composts and commercial fertilizers and soil amendments.

In the video introduction, Dr. Lamar states, “The New Standard Method for quantification of humic acids provides a more accurate and precise analysis compared to the existing regulatorily accepted methods, and it also provides a standard method for pure hydrophobic fulvic acid quantification. The advantage of this protocol is that it provides a gravimetric analysis of humic and hydrophobic fulvic acid concentrations on an ash-free basis, and the extraction process has been optimized to obtain the highest recoveries of both humic and fulvic acids from samples.

At the video’s conclusion, Dr. Monda states, “Following this procedure, the dry humic and fulvic acids obtained can be used for characterization purposes, such as the carbon-13 and the proton NMR electron resonance, and the ultrahigh resolution mass spectrometry, among other useful techniques. This can be used for characterization of the humus chemistry, as well as being a useful tool to dig deep into the structure-activity relationship with plant fitness and the underlying plant defense mechanisms.

Direct link to video on the JoVE Website: https://www.jove.com/v/61233/quantification-humic-fulvic-acids-humate-ores-doc-humified-materials (A free subscription will be required to view the entire video on the JoVE Website.)

From the JoVE Website: Filmed at the world’s top scientific institutions, JoVE videos bring to life the intricate details of cutting-edge experiments enabling efficient learning and replication of new research methods and technologies. JoVE is a peer-reviewed scientific video journal that is indexed in PubMed and Web of Science.

Effects of Humic Substances on Soil Microbes

By Richard Lamar, PhD
Senior Director of Humic Research
Bio Huma Netics, Inc.

Most of the work on agricultural applications of humic substances (HS) has focused on their biostimulant effects on plants. Far less work has been conducted on the effects of HS on soil microbial populations. It’s not surprising to learn, from the few studies that have been published, that HS also stimulate the growth of soil bacteria, even the bacteria that inhabit earthworm digestive tracts. One of the most important discoveries is that many species of soil bacteria are able to grow on humic acid (HA) as their sole carbon source (Tikhonov et al., 2010).

These findings have important implications for the roles played by soil bacterial communities—including those residing in the guts of soil fauna, such as earthworms—in the humification process (i.e., the process of conversion of dead plant tissues to humic substances). This means that these bacteria are consuming HS and modifying HS by metabolizing humic molecules and using the metabolized molecules to produce proteins, fats, and other types of molecules. When the bacteria die, they are in turn consumed by other microbes and those molecules created from metabolized humic molecules wind up being included as HS.

The other important piece of information that has come out of the work on bacterial-HS interactions is that, in addition to being potential carbon sources, HS can also act as soil bacterial growth stimulants or growth regulators (Tiknonov et al., 2010). This was demonstrated in a study in which a number of soil isolated bacterial species were grown on a medium that contained glucose as the carbon source (10 mg/ml) and humic acid (1 mg/ml). Thus, the humic acid was 10X lower than the glucose. Growth of the bacteria on this medium was compared with the growth of bacteria on a medium that did not contain the humic acid. The growth of 41% percent of the bacterial species (these were isolated from earthworm digestive tracts) were stimulated by the inclusion of the humic acid. The authors of the study concluded that, because the concentration of glucose was so high and the increase in available carbon from the addition of 1 mg/ml humic acid was insignificant, the humic acid acted as a growth stimulant to the 41% of bacteria whose growth was increased.

These types of studies have demonstrated that HS can stimulate the growth of plant-growth-promoting rhizobacteria (aka PGPR bacteria, for which the “rhizo” stands for rhizosphere or the area of soil that is intimately associated with plant roots). One of the most well-known PGPR bacteria are Pseudomonads, strains of which have been found to be able to solubilize phosphate, produce siderophores (important for Fe uptake), ammonia, and the plant-growth-regulator auxin (Gupta, 2008; Selvakumar et al., 2009).


Gupta, A. and M. Gopal. 2008. Siderophore production by plant growth promoting rhizobacteria. Indian J. Agric. Res. 42(2):153–156.

Salvakumar, G., P. Joshi, S. Nazim, P. K. Mishra, J. K. Bisht and H. S. Gupta. 2009. Phosphate solubilization and growth promotion by Pseudomonas fragi CS11RH1 (MTCC8984), a psychrotolerant bacterium isolated from a high-altitude Himalayan rhizosphere. Biologia, 64(2)239-245

Tikhonov, V. V., A. V. Yakushev, Y. A. Zavgorodnyaya, B. A. Byzov, and V. V. Demin. 2010. Effect of humic acids on the growth of bacteria.  European Soil Science, 43 (3):305–313.

BHN’s Lyndon Smith to Speak at New AG International Africa Conference

Bio Huma Netics, Inc., President and CEO Lyndon Smith has been selected to speak at the New AG International—Africa Conference, to be held April 6–8 in Marrakesh, Morocco. The full conference title is “A 360-Vision of Specialty Fertilizer, Precision Ag, Irrigation, and Biostimulant Developments in Africa.”

Mr. Smith’s presentation, titled “The biostimulant effect of humic substances: A case study in Africa,” will be given at 10 am on April 08. His presentation topics will include the following: the definition and classification of humic substances, atmospheric effects in soil, physiological effects in plants, and case studies with liquid solutions in dryland farming techniques.

More information on the conference is available at https://informaconnect.com/newagconference/.

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