What Are Humic Acids?
Humic acids are the water-soluble organic acids naturally present in
soil organic matter. Humic acids are a large family of organic compounds
with similar characteristics. They are defined by the process through
which they are isolated, rather than by a particular chemical
structure.
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I. Organic Matter in the soil exists in 3 different forms or states.
They are:
- Living plant and animal matter.
- Dead plant and animal matter.
- Decomposed plant and animal matter (Humus).
II. While it is true that all humus is organic matter, not all organic
matter is humus. For identifying characteristics of humus are:
- Its origin or parent material can no longer be identified.
- It must lose all its sugar, fiber, cellulose, lignin, protein, etc.
- It resists further decomposition.
- It is a minute amount of the parent material.
III. When organic matter decomposes to the point that it becomes humus,
then it can be further defined as:
- Humic - The portion of humus which is soluble and is called humic
acids.
- Non Humic - The portion of humus which is soluble and is called
humin.
IV. Just because organic matter may be defined as humus does not
necessarily mean that it is useable as humic acids or that it will have
any effect on the soil or the plants. The soluble humic acids have 3 major
fractions:
- Humic Acid - (singular) is a long chain molecule which is high in
molecular weight, dark brown and is soluble in an Alkaline solution.
- Ulmic Acid - Also called Hymatomelanic Acid.
- Fulvic Acid - is a short chain molecule which has a low molecular
weight, yellow in color and soluble in both acid and alkali.
Humic Acids Are
Not All Alike
Soluble humic acid products all produce
black liquids when dissolved in water. However, the properties and
activities of these black solutions are not necessarily alike.
Properties and activities of these of these
soluble fractions are dependent upon several factors:
- Type of organic material from which
derived.
- Reagent used to extract the soluble
fraction
- Conditions of storage of the finished
soluble product.
A. The organic raw material has
considerable effect on the final product. For example, higher or lower
organic content in the raw material will produce stronger or weaker final
extracts. The humic acids extracted will markedly differ as the raw
material varies in its state of oxidation (e.g. highly oxidated as with
peat vs. lower oxidation state as with Lignite coal.) Oxidation state of
the raw material has much to do with the cation exchange capacity (CEC) of
the humic acid extract, with lower CEC resulting from the less-highly oxidized
raw material (5-10 me/100 gm) vs. higher CEC's (well above 100 me/100 gm)
exhibited by extracts of more highly oxidation state, considerable
variation occurs within the Leonardite group. Also, a high silica content
in the raw material can interfere with alkaline extraction of its
contained humic acids.
B. Strength and pH extractant reagents will
affect not only the activity and properties, but will determine and
species of the resulting Humic product. For example, using a strongly
alkaline extractant, and maintaining the product at a high pH after
extraction will keep the humic, fulvic, and ulmic acids in solution. If
the product is acidified after extraction, or acid-extracted, the
predominant species remaining in solution will be fulvic and ulmic Acids,
as the majority of the humic acids will precipitate out.
C. Post-extraction storage is important to
properties and activities of a soluble humic acids product. For example,
if the post-extraction soluble product is maintained at an extremely high
pH for a period of time, the humic acid content will often drop
significantly. Low pH storage can result in precipitation of the humic
acid fraction of the product. In summary, variability in any of several
factors can produce humic acid products with widely different properties,
and activities which quite often are evident only after considerable use
experience. In addition, while several analytical methods for assaying
humic content of products are in use, no one method has yet been adopted
as "standard" by the industry and its regulators. Consequently,
it can be quite difficult to determine the efficacy of a humic acid
product by chemical testing alone; field-testing along with chemical
testing is recommend.
~by: Irvine L. Phillips, Jr. Micro-Chem International, Ltd, Nov. 15,
1989~
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