Humates in Hydroponics

Author G.Low and a member of the IHSS (International Humic Substance Society) closely collaborated on this story.

The result is an article that is without a doubt the most informed and comprehensive piece ever written on the subject of humates in hydroponics. If you really want to know your stuff get the Low down here.


Humates in Hydroponics


Commercial Humates are sourced from peat and coal formed over thousands or millions of years. They are formed during the coalification process from the degradation of organic material by microbial, chemical and geological action. Put simply, humates are various organic molecules of ancient compost.


‘Fulvic acid’ (FA) is the most important and active humate extract where hydroponics is concerned. It is water soluble and is chemically active and readily available for uptake by the plant.


Fulvic acid increases the absorption capacity of plant roots, aids the cell building process and enhances the passage of poorly transported ions into and throughout the plant’s cells by acting as an efficient organic chelator/complexing agent in hydroponic solutions.


Fulvic Acid Benefits

  • Enhances cell growth
  • Increases nutrient uptake
  • Increases nutrient transportation
  • Increases silica absorption
  • Stimulates plant immune system
  • Stimulates cell division
  • Enhances the permeability of cell membranes


Fulvic Acid and Chelation


Micronutrients are crucial partners (cofactors) of enzymes in every metabolic function of the plant. Respiration, photosynthesis, protein synthesis, energy transfer, cell division and cell elongation are all dependent on an adequate supply of calcium, iron, copper, manganese, magnesium, zinc and other micronutrients.


Many microelements in their basic form are unavailable to the plant. This is largely due to the fact that metal microelements such as iron, copper and zinc are positively charged (cations) while the pores (openings) on the plants’ leaves and roots are negatively charged. As a result the positive charges on microelements are repelled by the negative charged plant pores. As a result, there is a problem with the fixation of positively charged minerals at the negatively charged pores (the element can’t enter the plant due to the difference in charges).

Another reason that some microelements require chelating is due to their stability in solution. For instance, iron (Fe) is a reactive metal. In concentrated solution it will react with other fertilizer elements, particularly phosphorus (P) to form an insoluble compound. It forms the compound iron(III) phosphate which is a solid precipitate in water, so it falls out of solution. To prevent this happening Fe used in fertilizers is usually provided in the chelated form.


Well-formulated hydroponic nutrients ensure there is a high level of nutrient availability in the correct forms and ratios.  Nutrition that offers a diverse range of highly bioavailable elements will prove more effective than nutrition that has less diversity, particularly where the micronutrients are concerned. For this reason combinations of organic and synthetic chelates in hydroponic formulations are demonstrated to benefit yields.


Studies show that fulvic acid provides for excellent translocation of microelements, such as iron, throughout the plant. When added to an iron chelate in one study it stimulated more growth and better utilization of the iron than with the synthetically chelated iron (Fe EDTA) alone (Chen and Stevenson (1986) Soil organic matter interactions with trace elements).


FA use under conditions where adequate mineral nutrition exists consistently shows stimulation of plant growth when added to hydroponic nutrient solutions. Similar plant growth enhancements have been observed when FAs are applied to the foliage of plants grown in complete nutrient solutions. The degree of stimulation varies depending on the concentration of fulvic acid and on the quality/source of the fulvic acid (Plant Growth Stimulation by Fulvic Acids. K Day et al)


The common types of chelates used in hydroponic nutrients are the synthetic chelates, EDTA (ethylenediaminetetraacetic acid) and to a lesser extent DTPA (Diethylene triamine pentaacetic acid). Chelates such as EDTA and DTPA have a high affinity for e.g. iron and generally form stable complexes with the metal across a pH range from 4 to 7.


Chelates have several points of attachment with which they “grasp” the trace element. EDTA has four connecting points while DTPA has five. Higher numbers of connection points isn’t always an advantage. In some cases the four connection points may hold the element too tightly, while in different situations these may not hold it tight enough. For this reason, various chelates will prove more effective than others based on the ion that is chelated and the conditions in which the chelate is present.


For instance, the effectiveness of a chelating agent can depend on pH. In the case of iron Fe EDTA is best suited to slightly lower than neutral pH levels while Fe DTPA is most effective at higher pH values. DTPA is more costly than EDTA and less soluble and is usually found in higher quality fertilizers. DTPA is stable up to a pH of 7.5 while EDTA is stable up to a pH of approximately 6.5.


The most effective of the synthetic chelating agents is ethylenediaminedihydroxy-phenylaceticacid (EDDHA). However, it is important to note that EDDHA can only chelate with iron and not with other essential microelements such as Cu, Zn, Mn. Fe EDDHA is the most stable of all the commonly available iron chelates. This synthetic chelate is held in a bond up to 100 times tighter than DTPA because it has six molecular bonds rather than five bonds. Typically EDDHA is only found in premium fertilizers because of its higher cost. EDDHA is stable up to pH 9.0 (pH range = 4- 9) but is not suitable for foliar applications due to EDDHA only being absorbed through the roots of the plant.


As with the synthetic chelators, fulvic acid (FA) enhances the uptake of micronutrients due to its properties as an organic chelator.


Fulvic acid forms four-point bonds with the elements it chelates and can be absorbed into the plant. This adds to the mobility of nutrients. The nutrients chelated by fulvic acid can move more freely which prevents a number conditions like localized calcium deficiency that can occur due to low mobility of nutrients.


FA is a short chain molecule, which has a low molecular weight and soluble in both acid and alkali solutions/soils.


FA is effective when the growing environment in the root zone is above or below optimal levels. For this reason fulvic acid, more so than the synthetic chelators (EDTA, DTPA), retains its effectiveness under a range of pH conditions.


Chelated Minerals versus Complexed Minerals


Some nutrient elements only have the ability to be partially surrounded by a chelator/chelating agent and are referred to as a “complexes”, while those that are capable of being completely surrounded are termed chelates.


Confusion and often contradictory information exists surrounding chelated and complexed minerals. Terms such as amino acid complexes, amino acid chelates, polysaccharide complexes, lignosulfonate complexes, and amino proteinates abound. In some cases chelates are referred to as “complexed” or “chelate complexes” while in other cases fertilizer producers wrongly advertise complexed minerals as “chelated”. This only serves to confuse further. However, the difference between “chelated” and “complexed” can be understood via some basic principles.




In order for a compound to be called a true chelating agent, it must have certain chemical characteristics. This chelating compound must consist of at least two sites capable of donating electrons (coordinate covalent bond) to the metal it chelates. For true chelation to occur the donating atom(s) must also be in a position within the chelating molecule so that a formation of a ring with the metal ion can occur.


The term “complexed” originates from combinations of minerals and organic compounds that do not meet the guidelines of a true chelate.


The key difference between a chelated mineral and complexed mineral is that chelates are relatively more stable under adverse conditions while complexes are less thermostable and release the atom quickly under adverse conditions.


Not all nutrients can be chelated. The positively charged cations iron, zinc, copper, cobalt, nickel, manganese, calcium , magnesium, and potassium can be chelated while the negatively charged anions such as  phosphorous cannot.


While the negatively charged anions cannot be chelated they can be complexed via the use of donor atoms such as e.g. oxygen, nitrogen or sulphur. Amino acids such as glycine and/or lysergine are often used to complex the anions. Similarly, FA can be used to complex the negatively charged anions.



Both chelated and complexed minerals are more bioavailable than non-chelated and non-complexed minerals. This makes the use of additional organic (e.g. amino acid, fulvic acid, organic acids) and inorganic chelators/complexers highly beneficial in hydroponic formulations.


Humic Science




A polymer is a large molecule (macromolecule) composed of repeating structural units (monomers). These units are typically connected by covalent chemical bonds. Although the term polymer is sometimes taken to refer to plastics, it encompasses a large range of natural and synthetic materials with a wide variety of properties.


Because of the extraordinary range of properties of polymers, they play an essential and diverse role in everyday life.This role ranges from familiar synthetic plastics to natural biopolymers such as nucleic acids and proteins that are essential for life.


Aliphatic Compound


Relating to organic compounds where carbon atoms are linked in open chains, either straight or branched, rather than containing an aromatic ring. Alkanes, alkenes, and alkynes are all aliphatic compounds.


Aromatic Compound


Although the term aromatic originally concerned odour, today its use in organic chemistry is restricted to compounds that have carbon rings with particular electronic, structural, or chemical properties. Aromaticity results from particular bonding arrangements that cause certain electrons within a molecule to be strongly held.


Humic Substances


Humic substances (humic matter) are a complex group of naturally occurring heterogeneous (diverse) carbon based molecules produced from the degradation and decomposition (chemical & biological) of plant and animal organic matter.


This decomposition process that results in the formation of humic substances is known as humification. They are dynamic molecules forming polymers and constantly involved in biochemical reactions changing in physical, chemical and biological function. Because they undergo polymerization they form polymers (made of monomers or single sub units) of different lengths and combined with varying elemental compositions’ molecular weight varies greatly. Humic substances rapidly rearrange their molecular structure as the surrounding conditions change (Tombacz & Rice, 1999).


Humic substances possess both aromatic and aliphatic structural characteristics. The dominant functional groups are phenolic & carboxyl groups that contribute to the surface charge and reactivity of humic substances (Stevenson, 1994).


The first recognized study of humic substances was the work done by Achard (Achard, 1786), who extracted a dark, amorphous precipitate through a method of alkali extraction (solubilisation) and acidification. This work lead to the observation that more humic material could be extracted from the lower more decomposed (humified) layers of peat. Importantly it showed that humic matter was formed by the decomposition of organic material.


Decomposing organic material can be defined into two distinct groups. (1) Organic matter which is at various stages of decomposition where the morphology of starting organic material is still distinguishable, and; (2) the organic material has completely decomposed to the stage where none of the structure of the material which they formed from is visible. These two groups along with the fraction of non-decomposed dead and living organic material defines what is termed soil organic matter (SOM) or total organic matter.   This second group of completely decomposed organic material is referred to as humus. The name “humus” was introduced by De Saussure (De Saussure, 1804) to describe the organic dark coloured material found in soil.


Humis is the most important fraction found in soils and has been studied considerably. The interest is because of its pronounced effect on the physical, chemical and biological conditions of the soil (Russell & Russell 1950; Tan, 2000).


Humic matter and humus has become a very confusing subject because many scientists use terms like humic material, soil organic matter (SOM), humic substances and the like interchangeably. Current standards has humus defined into a humified and non-humified fraction (Stevenson, 1994). The non-humified fraction is made of many organic substances with definite chemical characteristics. The most common of these compounds are lignin, proteins (amino acids), carbohydrates, polysaccharides, waxes, melanin, cutin, nucleic acids, lipids and all of the biochemical compounds that have been synthesized by plants and soil microorganisms. These organic compounds are the sources for synthesis of humic substances (humified fraction) which are formed from further degradation and decomposition reactions in the process of humification.


It is important to note that soil organic matter (terrestrial) is not the only source of humic substances. Interest in humic substances has also lead to vast amounts of research on aquatic humic substances found in the waters of streams, oceans, lakes and their sediments. With humic matter making up a large proportion of deposits of peat, brown coal (lignite, leonardite), coal and shale. It is believed to be the most widely distributed source of organic carbon material on the surface of the earth.


As stated, humic substances are varied in molecular weight and elemental composition, dependent on the degree of polymerization, the starting organic material, environmental conditions and the chemical and biological processes of formation. The molecular weight is generally measured in Daltons (Da) which is an accepted alternative to the atomic mass unit. The unit of Daltons is mainly used in the life sciences as a measurement of molecular weight of polymers like proteins. Molecular weights of naturally occurring elements ranges from 1-238 g/mol, simple chemical compounds 10-1,000 g/mol and for polymers, proteins, DNA fragments 1,000-5,000,000 g/mol (1 Da = 1 g/mol). Although humic substances do form polymers they are reportedly held together by weak bonding. Humic material is a supramolecular structure of relatively small bio-organic molecules (having molecular mass <1000 Da). They are self-assembled mainly by weak dispersive forces such as Van der Waals force, π-π, and CH-π bonds into only apparently large molecular sizes (Piccolo, 2002).


Molecular weights are extremely important when discussing the efficiency of humates in hydroponics. This is because there is a limiting diameter in the pores and the walls of living plant cells through which molecules can freely pass. As a result large molecules (high molecular weight) are restricted from passing into the plant while smaller molecules (low molecular weight) can pass.  In simple terms, this means that fulvic acid (low molecular weight/small molecule) has a higher efficiency in hydroponics, while humic acid (high molecular weight/large molecule) has lower efficiency in hydroponics – or at least this is the case where bioavailability, plant uptake, cell membranes and translocation is concerned.


This information becomes important when understanding “the degree of stimulation (exhibited by FA in hydroponics) varies depending on the concentration of fulvic acid and on the quality/source of the fulvic acid”. (Plant Growth Stimulation by Fulvic Acids. K Day et al)


Below are illustrations of hypothetical molecules of fulvic and humic acid.


Fulvic Acid- Figure 1: Typical Structure of Fulvic Acid




As adapted from the proposed structure of fulvic acid by Buffle 1977


Humic Acid- Figure 2: Hypothetical Structure of Humic Acid Showing Functional Groups and Bridge Units Variously Placed on Aromatic Rings



As adapted from the proposed structure of humic acid by F.J. Stevenson 1982


These diagrams make it easier to envision the idea of molecular size and how it influences humic and fulvic’s efficiency in hydroponic systems.  I.e. you will note that humic acid has a far larger molecular structure than fulvic acid.


Fulvic Acid Products


Figure 3: Classification and Chemical Properties of Humic Substance



As adapted from F.J. Stevenson and J.H.A Butler


We have established that molecule size dictates certain desirable properties for humic and fulvic acid. Figure 3 illustrates that there is a direct correlation between colour and size. Put simply, the key to identifying a quality fulvic acid product is its’ colour. At dilution high quality fulvic acid will be a light yellow to an orange colour. Any product that is dark brown is less suitable for use in hydroponics due to it containing a higher percentage of humic acid.


Having said this, humic/fulvic science can be too easily oversimplified and from a scientific perspective, both humic acid and fulvic acid can be used in hydroponic systems benefiting the growth and yield of plants. HA does, although, have several limitations because of it’s chemical and physical properties. HA will chelate and form complexes with metal ions but this can lead to the precipitation of HA especially with regards to the higher molecular weight fractions of the HA. Metal ions can create linking of HA molecules leading to precipitation (non colloidal). HA molecules of higher molecular weight are already insoluble due to the pH of a solvent they are in and considering most nutrient solutions in hydroponic systems are used at a pH lower than 7.0 this limits the solubility of a large proportion of HA that has been extracted usually up to a pH of 10-11. This not only results in the precipitation of HA’s but also non humified organic material is also susceptible to precipitation. Depending on the ionic strength of the solution this can lead to the coiling of HA and resultant precipitation. Due to this, metal complexes of fulvic acid are in general more bioavailable than those of humic acids.


Generally the use of FA as a chemical carrier and biostimulant in hydroponics far exceeds the suitability of HA. The use of HA still has benefits but a large proportion of the HA is unsuitable because of solubility characteristics and the potential risk of locking up and precipitation of trace metal ions required for utilization by the plant. This is variable by the products source material and extraction methods. It is possible to produce a HA product suitable for use in hydroponics but an actual product developed specifically for this use is unknown to the author and possibly unlikely because of the limited markets. Products used in the hydroponics market are the result of normal HA extraction methods designed to be viable in conventional agricultural markets. By definition a properly extracted FA is suitable for use in any agricultural production whether for soil, foliar, fertigation or soilless culture. It’s range of compatibility in products or as an additive is far wider with HA suited to more specific product applications and in the soil because of low compatibility.


Fulvic acid displays highly acidic properties and is relatively the smallest in molecular size of the major types of humic substances. It is a hydrophilic colloidal, amorphous (non-crystalline forming) material with a yellow to brown color. According to research the number-average molecular weight is reported to be from 175 to 3,750 daltons (Shnitzer and Skinner, 1968). FA was often in and out of favour and during the 60’s and 70’s the interest in researching FA waned. The opinion of Stevenson (1994) was that this is due to difficulties in recovering FA from acidified extracts of soil because of the inorganic contaminants. In removing these inorganic contaminants to purify the FA there is a considerable loss of the FA. Hence be wary of claims of the most pure fulvic acid as there are generally several impurities. When FA was discovered in aquatic environments where it is the more dominant of the humic substances interest was considerably increased. It is still uncertain as to whether FA is a precusor (building block) of HA formation or it is the resulting product of degradation of humic acid.


Using various methods researchers have fractioned fulvic acid in to various groups over many years with names like crenic acid and aprocrenic acid. Currently fulvic acid can be isolated to the following fractions: High molecular weight fraction, Generic high molecular weight fraction, Low molecular weight fraction, Generic Low molecular weight fraction, Fractions A, B, C, and D (K.H. Tan, 2003).


Production and Testing of FA Products


The methods of producing HA and FA for agricultural applications is governed by economics as opposed to the methods used for the qualitative and quantitative study of chemical structure, biological and chemical function. Among other things, the source or raw material governs the quality and quantity of what is extracted. There are sources of humic substances throughout the environment but the source material for extraction not only needs to be high in HA and/or FA content but also the HA has to be an easily soluble material.


As there are no real standards in the world for HA and FA used in agriculture there is a lot of misconception and deception in the market place. Marketing of fulvic acid is currently the most deceptive because of the lack of standards. Generally speaking, with regards to many humic/fulvic products HA content is often 5-10% below the analysis the product is sold with and in the case of FA there are typically even more irregularities.


To compound the problem, the way a humic/fulvic product is described, guaranteed and marketed is often governed by the various regulatory departments who oversee agricultural product registrations. To date there is no “standardized” analytical method for quantification and accepted labeling practices often vary greatly from state to state and province to province in various countries. For example, in California and Oregon the term fulvic acid is not allowed to be used on any product label. Instead these agencies consider fulvic and humic acid the same substance and require that only humic acid be listed on labels. Tests for humic/fulvic in these states (known as the ‘California Method’) utilise a strong base (NaOH) that separates the humic and the fulvic fractions. The fulvic solution is then discarded and the remaining material which consists of humic acid and impurities is measured. Products with a high percentage of fulvic acid are hit particularly hard by this very inaccurate method of testing and in fact inferior products (i.e. products with high humic and low fulvic) test much better.


Accurately testing FA percentage is very expensive because of the consumables used and the length of time required in testing. There are also very few accredited laboratories around the world that perform this type of analysis. The only accurate way to test is via analytical testing using a credible scientific method that uses a polymeric adsorbent (ion exchange resin). For this reason many manufacturers don’t test or use unreliable testing procedures (e.g. the California Method) and therefore FA/humic percentages are not accurately assayed.


Significant searches of suppliers around the world can result in the sourcing of fulvic powders of fairly high quality that can be easily evaluated visually. They are light yellow to orange in color but you must also be careful not to confuse these with fulvic-amino acid products now being offered by a number of manufacturers where the high amino acid content results in a much lighter coloured fulvic product. These powders are typically light yellow but are low in FA content.


With new breakthroughs in humic research comes new products. One new technology is the extraction of HA (Vusumzi, 2006) and FA from black liquor which is a by-product of the wood pulping industry. Currently the author knows of two companies that are producing humic substances (HA & FA) from black liquor with several more looking at this as a source. This idea came about because of the environmental push to reduce the waste produced in pulping and paper production, a high energy and high chemical input industry.


Fulvic Acid – Optimum ppm in Solution


Research has demonstrated that optimum ppm for fulvic acid in hydroponic applications ranges between 25-300ppm (very dependent on what other chelators are present but let’s not get too complex for now). I recommend FA use at between 40-50ppm where standard, chelated hydroponic nutrients are used.


If you need to work out how to achieve 40-50ppm of fulvic acid in solution you use this equation.


The Dilution Volume =                    The Concentration You Want  X   The Volume You Want


The Concentration You Have


I.e. the equation is, the concentration you want times the volume you want, divided by the concentration you have. Actually, perhaps we need an example.


Strictly speaking this equation is used to establish how many ml or grams would be used to achieve a given ppm in solution.


V1 = C2 x V2




This comes from the dilution/concentration equation of  C1 x V1 =  C2 x V2


C stands for concentration and V stands for volume. 1 refers to stock, and 2 refers to diluted solution.


C1 = Initial Concentration (80,000mg/L)

V1 = Initial Volume (unknown)

C2 = Final Concentration (50mg/L = 50ppm)

V2 = Final Volume (1 Litre)


Let’s say that we had an 8% fulvic acid product that is listed as percentage weight by volume (%w/v) and we want to work out how much of our FA product is required to achieve 50ppm of FA in solution.


That’s 8 (%) x 1000 divided by 100 = 80g/L of FA in solution. I.e. 8% w/v equals 80 grams of FA per litre.


The next thing we need to do is to convert the units of measurement into ppm. Keep in mind that 1ppm equals 1mg/L and that ppm and mg/L are the same thing with different units of expression.


Keep in mind also that 1 gram = 1000mg or 1000ppm. (1000ppm in 1 Litre – parts per million is like a %age of something)


Therefore, 80g/L = 80,000mg/L = 80,000 ppm.


The initial volume is the amount that you need to make up to the final volume and the final volume is 1 litre.


Using the equation;  C1 x V1 = C2 x V2


80,000 x V1 = 50 x 1


V1 = 50 x 1 divided by 80,000


V1 = 0.000625 (Litres)


To Convert Litres to mL X 1,000


0.000625 x 1000 = 0.625 ml/L


Therefore, to achieve 50ppm of FA in solution you would need 0.625mL / Litre of an 8% w/v FA additive or 6.25ml per 10 litres.


This equation can be used for working out all sorts of dilution rates in order to achieve a given ppm, %w/v or mg/L in a final solution.






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