Humic Acid

GIRL OR BOY? New Fulvic Acids Research

Early in my career I read a claim about an ancient Egyptian belief. These ancient people were thought to believe that if the urine of a pregnant woman increased the growth of wheat she would have a girl, and if it increased the growth of barley she would have a boy.

I tested this concept with diluted urine (so that the minerals would not affect plant growth) and found that it was not true for modern wheat and barley, and probably also not true for ancient wheat and barley. However, what I discovered was that two minor hormones in the urine of a pregnant woman (pregnanetriol and pregnenolone) increased the growth of barley by a substantial amount of about 10%. The urine of a pregnant woman contains a large amount of pregnanediol, but this had no effect on barley. Further, the diluted urine had no effect at all on wheat.

Many years later I tested the foliar application of dilute fulvic acids on soybean plants. There had already been many claims by fulvic acids vendors that such foliar applications substantially increased plant growth. I was sceptical of such claims and therefore did my own test. I was surprised to find that the fulvic acids increased the growth of soybeans by about 10%. Other ingredients including contaminants in the fulvic acids were too dilute to give such a relatively large increase in growth, so the only reasonable explanation was that fulvic acids act like a hormone, analogous to the situation described above where progesterone hormones increased barley growth.

An important question is whether fulvic acids are a general plant hormone, and research needs to be done to check this. The concentration of fulvic acids that I used for foliar application was quite low and therefore very cost effective for agriculture. In addition, other fulvic acids research also needs to be done due to the paucity of knowledge about fulvic acids, and I will give some insight into this below.


1. What are Fulvic Acids?

A cynical but true answer would be: “God only knows!”

2. What is my definition of Fulvic Acids?

A yellow-brown substance that dissolves in 0.1 M hydrochloric acid and is retained on an XAD-7 resin that has been equilibrated with 0.1 M hydrochloric acid. It has a fluorescence much stronger than humic acids, but with a similar emission spectrum (max. 420-440 nm at an excitation of 340 nm).

3. Is there a satisfactory Fulvic Acids analysis available?

No. Manufacturers generally measure the visible light spectrum, but unless one already knows that the fulvic acids is of high purity, the test is inaccurate. Fluorescence emission at 400 to 600 nm with an excitation of 340 nm is far more accurate.

4. Are there Fulvic Acids standards to perform fluorescence analysis?

No. (I have developed a method to obtain pure fulvic acids according to my definition above, but have not commercialized it. Perhaps there is a 3rd party that is interested in this.)

5. How are Fulvic Acids obtained?

The most common source of fulvic acids is direct extraction from peat bogs. Lignite coal can also be slowly oxidized in air to form fulvic acids, which are then extracted by methods that are usually trade secrets. Note that contrary to manufacturer’s claims, I have never found more than trace amounts of fulvic acids in humic acids obtained from lignite coals.

6. Can Fulvic Acids be obtained from microbiological processes?

In recent years numerous manufacturers have started to market fulvic acids that are far cheaper than the traditional fulvic acids obtained from peat bogs or the oxidation of lignite coals as described above. These “fulvic acids” are by-products of microbiological processes. They are colored compounds that probably comply with the visible light absorbance as described above, and in that sense fall within the loose definition of fulvic acids. However, I have found their composition to be extremely variable and they may not necessarily be adsorbed onto an XAD-7 resin as described above.

Whether or not these by-products contain fulvic acids may not be important if the products enhance plant growth. If such enhancement occurs it would probably be through a plant hormone-type effect. I have not seen trials that demonstrate this, but concede that they may exist.

7. Can Humic Acids be converted to Fulvic Acids?

Yes. I have done very little humic/fulvic acids research in recent years, but occasionally I investigate some matters. Recently I discovered that humic acids slowly convert to fulvic acids under solvent extraction methods. First, the humic acids are dissolved in dilute alkali such as 0.1 M sodium hydroxide, and are then left in contact with solvents of decreasing polarity. Smaller and smaller fractions of the original humic acids become soluble with decreasing solvent polarity, but even a small amount is soluble in n-hexane.

8. How is the conversion of Humic Acids to Fulvic Acids explained?

I believe that neighboring carboxyl and hydroxyl groups within a humic acid molecule slowly react with each other to form a lactone or hydroxy lactone, which are cyclic esters. This esterification process then makes the molecule more hydrophobic and soluble in organic solvents. The humic acids then become fulvic acids. The more lactones that form within the molecule compared to remaining free carboxyl and hydroxyl groups, the more hydrophobic the compound is, and those molecules that dissolve in n-hexane probably contain only lactones and no carboxylic acid or hydroxyl groups at all.


In the section of this website entitled “Structure and Origin of Humic Acids and their Relationship to Kerogen, Petroleum, Bitumen and Coal”, I made the following statement from work that was done with fulvic acids in 1993 and published in 2003:

“A fulvic acid reacted with acetic anhydride/ pyridine (3:1), but not butylated, showed major IR bands for CH2, CH3, lactone, and acetate groups, and only very minor H2O bands. The spectrum is shown in Fig. 10, highlighting the lactone and acetate bands.”

This was accompanied by Figure 10:

Acetic anhydride/pyridine (3:1) is a good solvent for giving both acetate esters and lactones. The 1776 cm-1 solution IR band is due to lactone, and the 1737 cm-1 band is due to acetate. In conjunction with these data, the latest research demonstrates that fulvic acids are simply humic acids with lactone groups in place of separate carboxylic acid and hydroxyl groups.

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