Humic acid is a mixture of various high-molecular organic weak acids formed by the decomposition and transformation of animal and plant residues through microbial decomposition and transformation and a long geophysical and chemical transformation process. It is rich in various active functional groups such as carboxyl, hydroxyl, methoxy, carbonyl, and quinone.
The main elements of humic acid are carbon, hydrogen, oxygen, nitrogen, and sulfur. It is a polycondensate of polyvalent phenolic aromatic compounds and nitrogen compounds. It is widely distributed in low-grade coal, soil, water sediments, animal feces, organic fertilizers, animal and plant residues, etc.
The basic structure of humic acid macromolecules is aromatic rings and alicyclic rings, with carboxyl, hydroxyl, carbonyl, quinone, methoxy and other functional groups attached to the rings. It has exchange, adsorption, complexation, chelation and other effects with metal ions. In a dispersed system, it acts as a polyelectrolyte and has the effects of coagulation, peptization, and dispersion. There are also a certain number of free radicals on the humic acid molecule, which is physiologically active.
Effects of humic acid:
1. Direct effect:
Promote plant growth and increase crop yields
2. Indirect effect
① Physical effect
- Improve soil structure;
- Prevent soil cracking and erosion;
- Increase soil water holding capacity and improve cold resistance;
- Darken the soil color, which is conducive to solar energy absorption.
② Chemical effect
- Regulate soil pH;
- Improve and optimize plant absorption of nutrients and water;
- Increase soil buffering capacity;
- Under alkaline conditions, it is a natural chelating agent (chelates with metal ions to promote their absorption by plants);
- Rich in organic matter and minerals necessary for plant growth;
- Increase the solubility of organic fertilizers and reduce fertilizer loss;
- Convert nutrients into a state that is easily absorbed by plants;
Humic acid can enhance plant absorption of nitrogen, reduce phosphorus fixation, and can protect and store nitrogen, phosphorus, potassium and other elements deep in the soil in the soil, and can accelerate the process of nutrients entering the plant body, improve the application effect of inorganic fertilizers, so humic acid is a “reserve” of plant nutrients and physiologically active substances.
③ Biological effects
- Stimulate the growth and reproduction of beneficial microorganisms in the soil;
- Contains a variety of active functional genes, which can enhance the activity of catalase and polyphenol oxidase in crops, stimulate physiological metabolism, and promote growth and development;
- Can reduce the opening intensity of plant leaves’ stomata, reduce leaf transpiration, thereby reducing water consumption, improving the water status of plants, ensuring the normal growth and development of crops under drought conditions, and enhancing drought resistance;
- Humic acid is mostly amphoteric colloids with high surface activity, which has an inhibitory effect on fungi, can enhance the cold resistance of crops, is easily adsorbed by cell membranes, changes cell membrane permeability, promotes the absorption of inorganic nutrients, prevents rot and root rot, and reduces diseases and insect pests;
- Humic acid can form complexes or chelates with trace elements, adjust the ratio and balance of macroelements and trace elements, and strengthen the synthesis and operation of enzymes on sugars, starch, protein, fat and various vitamins. It can promote enzyme activity, convert polysaccharides into soluble monosaccharides, increase the synthesis and accumulation of starch, protein, and fat substances, and accelerate the movement of primary products of various metabolisms from stems, leaves or roots to fruits and seeds, making the fruits plump and thick.
A large number of studies have shown that humic acid is a close friend of inorganic fertilizers, a slow-release agent and stabilizer for nitrogen fertilizers, a synergist for phosphorus fertilizers, a protective agent for potassium fertilizers, a regulator and chelating agent for medium and trace elements, and humic acid has a significant synergistic effect on chemical fertilizers.
