A Good Helper for Agricultural Production - Humic Acid Fertilizer
I. What is Humic Acid?
Humic acid is a large molecular organic compound mainly formed in nature through the microbial degradation of animal and plant residues and microbial bodies, combined with a series of physical and chemical reactions. The compound contains a large amount of organic acid parts, phenols, aromatic hydrocarbons, fatty acid tails and amino acid residues, and is mainly composed of carbon, hydrogen, oxygen, nitrogen and other elements. The complex structure and composition elements also bring it many properties.
II. Enhancement Mechanism of Humic Acid Fertilizers
Due to its special structure and composition, humic acid has natural superiority over ordinary fertilizers when combined with them.
Firstly, some small-molecule humic acids themselves can be absorbed and utilized by plants as organic matter, serving as nutrients or hormone-like substances to regulate the metabolism within plants. Due to the ability of humic acids to undergo complex chemical reactions such as chelation with various substances, they can slowly release nitrogen, phosphorus, and potassium fertilizers, thereby regulating the nutrients in the soil and fertilizers and reducing fertilizer waste.
For nitrogen fertilizer, humic acid can make rational use of nitrogen through its own structural characteristics. All the oxygen-containing functional groups of humic acid can react chemically with urea to form stable chemical bonds. The reaction between humic acid and nitrogen results in the formation of humate ammonium, which fixes the nitrogen in the urea solution and reduces the amount of ammonia volatilization and leaching.
Humic acid is also a potential inhibitor of urease. Due to the presence of polyphenol oxides in it, it can inhibit the activity of urease, reduce the rate of urea hydrolysis, and increase the utilization rate of urea in the soil. Some other studies have shown that in acidic soil, HA can act as an extracellular electron mediator to participate in the metabolic process of nitrogen-fixing microorganisms, providing electrons for these nitrogen-fixing microorganisms.
Phosphorus fertilizer can promote the growth of crop roots, enhance the cold and drought resistance of crops, and also increase the number of grains and the number of full-grain seeds. However, phosphorus in the soil is easily fixed by calcium and magnesium (in alkaline soil) or iron and aluminum (in acidic soil). At this time, humic acid can utilize its ion exchange effect to compete for the adsorption sites of phosphorus, reducing the fixation of available phosphorus in the soil.
Potassium fertilizer can promote the healthy growth of crops, enhance their stress-resistance ability, and facilitate the formation of sugar and starch. The acidic functional groups of humic acid have the function of storing and absorbing potassium, which can prevent the fixation of potassium by clay minerals and improve the fertility of potassium fertilizer.
III. The Effects of Humic Acid on Plants and Soil
Humic acid, when used as a fertilizer, can be well absorbed by the roots of crops, increasing the emergence rate and survival rate of the crops, and promoting the growth and development of the crop roots, as well as enhancing the crops' ability to absorb water and nutrients.
Humic acid, as an organic chemical aggregate substance with multiple acidic functional groups and a high specific surface area, can be decomposed by the organic acids secreted by plant roots, and then form small molecule substances that plants can absorb. This increases the bud sites of lateral roots on the plant and promotes the growth of the root system.
Humic acid can also enhance the stress-resistance ability of plants. For instance, humic acid can reduce the opening degree of stomata on leaves, thereby reducing water evaporation and enabling plants and soil to retain more water, thereby strengthening the plants' resistance. Under stressful conditions, applying humic acid can activate and produce a large amount of superoxide dismutase, peroxidase and peroxidase. These enzymes regulate plant metabolism through the antioxidant enzyme system, reduce the permeability of the cell membrane, thereby alleviating the damage caused by stress to the plants and promoting plant growth.
Humic acid contains plant hormone-like substances, which can participate in regulating the germination of plant seeds and enhancing their photosynthesis. These hormones can penetrate into the plants, regulate the expression of genes, and alter the structure of functional proteins.
Most of the soils in the world lack humus. This is because natural HA is formed through the slow microbial metabolism of biomass. Even under the best chemical activity conditions, it takes more than 15 years.
Due to continuous farming or excessive planting of incorrect crops and sequences, the soil structure in farmland has been severely damaged. This process accelerates the oxidation loss of soil organic matter and the reduction of large pores. At this time, by taking advantage of the colloid properties of humic acid, larger "soft" aggregates can be promoted to form, gathering the dispersed soil particles and forming a large number of soil micro-aggregates, thereby improving soil permeability.
Humic acid is a highly active component of organic carbon. Humic acid itself is dark in color, which is conducive to absorbing solar heat energy. When humic acid is decomposed by microorganisms, it releases heat. Especially in early spring, when the seedlings of warm-loving crops just break through the soil, it can raise the soil temperature and play a role in resisting the spring cold.
Humic acid fertilizer combined with earthworm manure can improve soil aggregates, increase soil salt leaching, and inhibit nitrogen loss. The improvement of the stability of large aggregates and the microstructure of the microscopic structure of aggregates affects the bacterial community in large aggregates by increasing the relative abundance of aerobic heterotrophic bacteria (such as Rhodobacteraceae and Bacteroidaceae).
In conclusion, by adding an appropriate amount of humic acid to common fertilizers for application, it is possible to change the past technology that solely relied on regulating the fertilizer's nutritional functions to improve fertilizer efficacy. This enables a comprehensive and integrated regulation and enhancement of the "fertilizer nutrition - crop absorption - soil environmental function" as a whole.
Humic acid, as an important component for achieving green agriculture, is applied in the following ways: (1) improving the physical and chemical properties of the soil, enhancing soil activity and fertility; (2) promoting plant growth and improving crop quality; (3) through the multiple properties of humic acid itself, it can play a role in soil remediation through redox reactions and adsorption; (4) after entering the soil in the form of fertilizer, humic acid can become a growth substrate for microorganisms, having positive effects on soil carbon cycling and plant metabolism.
