Exploring Humic Acid: Structure and Classification Explained – Part 1
Introduction
In the pursuit of sustainable agriculture and improved soil health, humic substances—especially dry humic acid—have emerged as essential tools. Derived from the decomposition of natural organic matter, humic acid contains multiple functional groups that enhance nutrient retention, stimulate microbial activity, and improve soil structure. In this Part 1, we explore the structure, origin, and classification of humic acid and its derivatives.
1. Humic Acid
Humic acid is a non-homogeneous aliphatic-aromatic macromolecular organic weak acid mixture, rich in carboxyl, phenolic hydroxyl, quinone, carbonyl, and methoxy functional groups. It is formed through the decomposition and synthesis of plant and animal residues—mainly plant matter—by microbial activity and long-term geophysical and chemical processes.
2. Fulvic Acid
A component of humic acid with relatively low molecular weight. It is soluble in dilute alkali, acid, and water, and appears yellow or brownish-yellow in solution. Fulvic acid is the most active and mobile fraction of humic substances.
3. Free Humic Acid
This refers to humic acid in a protonated acid form, which can be extracted from raw materials or products using dilute alkaline solutions.
4. Combined Humic Acid
A type of humic acid whose acidic functional groups are bound to metal ions, forming humate salts. It can be extracted using sodium pyrophosphate solution.
5. Total Humic Acid
Total humic acid includes both free and combined forms. It is commonly extracted after acid washing to remove metal ions and soluble salts, followed by alkaline extraction.
These are humate salts soluble in water at room temperature, containing fulvic acid and its derivatives. Most commercial formulations are based on dry humic acid.
7. Water-Soluble Humic Acid Salts
These are humate salts that dissolve in water but precipitate under pH = 1 conditions. They are important markers of humic content in fertilizer products.
8. Soluble Humic Acid
Humic acid extracted with water and precipitated by acid, present in ionic form in the extract. It is a key indicator in evaluating humic fertilizers and humate products.
9. Potassium Humate
A humate salt produced from the reaction between humic acid and potassium hydroxide. It contains potassium fulvate and is widely used in agriculture. Often made from dry humic acid, it improves potassium availability and enhances soil structure.
10. Sodium Humate
Formed by reacting humic acid with sodium hydroxide. It contains sodium fulvate and is used in agriculture, wastewater treatment, and animal feed. A common application of dry humic acid.
11. Ammonium Humate
A humate salt produced by the reaction of humic acid with ammonia. It contains ammonium fulvate and provides nitrogen to plants.
This article is only part of the full series. If you’d like to read the complete guide, stay tuned for our next installment in this series.
Exploring Humic Acid: Structure and Classification Explained – Part 2
Sodium humate uses in livestock farming and aquaculture
