An Introduction to Humic Acid Knowledge

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Humus is the main component of soil organic matter, accounting for approximately 85%-90% of its total amount. Soil humus is the main substance that improves soil properties and provides nutrients for crops, and it is a key indicator of soil fertility levels. Therefore, applying more humic acid fertilizers (abbreviated as humus fertilizers) is an effective technical measure to increase the organic matter content in the soil. I. What is humic acid? Humic acid is a natural organic substance that results from the decomposition and synthesis of ancient plants by microorganisms. It possesses properties such as weak acidity, water absorption capacity, colloidal nature, adsorption ability, ion exchange capability, chelating ability, redox properties, and physiological activity. Based on the molecular weight and solubility of humic acids, they are classified into fulvic acid, brown humic acid, and black humic acid. Humic acid is widely used in agricultural production due to its low molecular weight, numerous acidic groups, solubility in acids, bases, and water, and ease of absorption by plants. Currently, the main products used in agricultural production include: humic acid (huangfu acid)-based organic-inorganic compound fertilizers, liquid fertilizers made from huangfu acid, plant hormones, soil conditioners, drought resistance agents, pesticides with enhanced efficacy, as well as veterinary drugs and feed additives. II. Forms and functions of humic acid in soil: Due to its strong adsorption capacity, free humic acid constitutes only a very small portion in the soil; it mainly forms stable salts by combining with strong bases, creates complex gels by reacting with hydrated oxides, and binds with clay particles to form colloidal complexes. In short, in the soil, humic acid combines with mineral colloids to form inorganic-organic composite colloids in the soil. Humic acid possesses excellent absorption and substitution capabilities as well as buffering capacity; it has a significant impact on the physicochemical properties of soil, markedly enhancing its ability to retain nutrients and water. This is why soils with a high organic matter content have a large water retention capacity and strong fertility retention. It can be seen that increasing the humic acid content in the soil is an important measure to improve soil fertility. III. The functions and application of compost 1. Improving soil: The humic acid organic colloids in compost form gel-like substances in the soil, which bind soil particles together and increase the water-stable aggregates in the soil. This helps to regulate the balance of water, nutrients, air, and temperature in the soil, and it is very effective in improving infertile soils that are either too sandy or too clayey, thereby enhancing the ecological environment for crops. In the improvement of saline-alkali soils, humic acid is effective due to its high content of active functional groups and large base exchange capacity; it enables the adsorption and retention of a large amount of harmful cations in the soluble salts in the soil, thereby reducing soil salt concentrations and lowering the pH of saline-alkali soils. Thereby improving the ecological environment of crops. 2. Improving fertilizer efficiency: Since humic acid can adsorb, exchange, and activate various mineral elements in the soil, such as phosphorus, potassium, calcium, magnesium, etc., it increases the availability of these elements, thereby improving the nutritional conditions for crops. It acts as a synergist in fertilizers, and reduces the adverse effects of fertilizers on the physical and chemical properties of the soil. The benefit of nitrogen fertilizers lies in their ability to reduce nitrogen volatilization losses; their effect on urea is particularly significant, as it allows the fertilizer efficiency of urea to be extended. Promotes nitrogen absorption and improves the utilization efficiency of nitrogen fertilizers. The mineralization rate of organic nitrogen in the soil increases, leading to an elevation in the content of readily available nitrogen in the soil. The synergistic effect on phosphate fertilizers is manifested in reducing the fixation of readily available phosphorus by the soil, thereby playing a role in releasing phosphorus. It converts insoluble phosphorus in the soil into available phosphorus, thereby promoting crop uptake of phosphorus. It improves the effective utilization rate of phosphatic fertilizers, promotes the conversion of organic and inorganic phosphorus in the soil, increases the movement distance of phosphorus within the soil, and stimulates the development of crop roots. The synergistic effect of potassium fertilizer is manifested in its ability to reduce the uptake and fixation of potassium in the soil, thereby increasing the utilization rate of readily available potassium. It promotes the release of insoluble potassium and increases the amount of readily available potassium, which can mitigate the negative effects of potassium fertilizers on the soil and crops, and has a positive effect on improving crop quality. Humic acid also has a significant synergistic effect on trace elements. 3. Stimulating crop growth: Humic acid contains various functional groups, and as a physiologically active substance, it stimulates the growth and development of crops as well as their internal physiological metabolism; inorganic fertilizers do not possess this property. Huanghumic acid, which is the low-molecular-weight component of humic acids, is water-soluble. It not only has a significant stimulatory effect on various crops when used in methods such as seed dressing, root dipping, and spraying, but it also exerts a stimulating effect once absorbed by the roots. It promotes seed germination and increases the emergence rate and survival rate of seedlings. It has a special promoting effect on crop root development, accelerating root formation in seedlings, increasing the number of lateral roots and overall root mass, as well as promoting root elongation, thereby enhancing the crops’ ability to absorb water and nutrients. The stimulatory effect of humic acid is manifested in the above-ground parts of crops as vigorous growth, increased plant height, and stronger stems, with effects being particularly evident in the early stages. Humic acid is absorbed through plant roots and stimulates the physiological metabolism of plant cells, as evidenced by an increase in respiration intensity and photosynthetic activity. Spraying humic acid on crop leaves results in a reduction in the opening degree of leaf stomata, a decrease in water transpiration, and an increase in enzyme activity in the crop roots. 4. Disease resistance: A high content of organic matter in the soil provides an excellent environment for beneficial microorganisms; these beneficial organisms gradually become dominant, suppressing the growth of harmful pathogens. Additionally, plants grow stronger due to the favorable soil conditions, which enhances their disease resistance. As a result, **diseases, especially those transmitted through the soil, are reduced. 5. It can enhance the stress resistance of crops. Factors such as soil, moisture, nutrients, temperature, light, and air in the growing environment of crops constitute the conditions under which plants grow. Humic acid acts as a buffer, reducing the adverse effects on crop growth and thereby contributing to their stress resistance. It can enhance the drought resistance of crops, increasing water conservation efficiency by 30%. The effect of water conservation and soil moisture retention is second only to that achieved by plastic mulching. To enhance the cold resistance of crops, using humic acid compound fertilizers or applying humic acid via foliar spraying can both improve the resilience of winter crops. It has the ability to defend against pests and diseases; humic acid exhibits unique effects in preventing and controlling them. When used in combination with pesticides, it has antibacterial and disease-resistant properties (for example, mixing it with jingangmycin enhances its effectiveness). 6. It can improve crop quality. The impact of humic acid on improving crop quality will be very significant. In vegetables and fruits, it can increase sugar content, raise vitamin C levels, and reduce the acidity of the fruit. In broadleaf crops such as tobacco and vegetables, it can improve the quality of the leaves. In food crops, it promotes the presence of higher amounts of low-molecular-weight organic nutrients in the crops. IV. Classification of humic acids 1. Mineral humic acids: These are humic acids directly extracted from minerals such as peat and coal through specific processes. The humic acid content increases gradually, from bryophyte peat to herbaceous peat and then to woody peat. 2. Biochemical humic acid (BFA): It is produced from agricultural waste such as crop straws, wood chips, and bagasse through a special microbial fermentation process. It is rich in humic acid, as well as amino acids and various microbial communities; it is a mixture that can be regarded as the green hero of modern agriculture. Humic acid liquid fertilizers (including foliar fertilizers, top-dressing fertilizers, drip irrigation fertilizers, etc.) are formulated using monovalent salts of FA or HA as the water-soluble organic matrix, along with N, P, K, and trace elements. Such products not only provide quick-acting nutrients but also exert the biological activity of HA substances. They feature low application costs, high added value, ease of use, and rapid results, which makes them very popular among users and has turned them into the main types of HA products in fierce competition on the international market in recent years. Products such as K67 and KOMIX produced in the United States using lignite, and the \"Leaf Vitality Sprayer\" made in Japan using lignite NHA, were all quite famous at one time. Brands such as “Ye Mian Bao”, “Pen Shi Bao”, “Nong Jia Bao”, and “Hui Man Feng”, which were developed in our country at the end of the last century, are also quite influential. In recent years, HA liquid fertilizers have developed rapidly, becoming an important supplementary product to conventional fertilizers; they also play a significant role in the development of green and ecological agriculture. In the text, FA refers to humic acid, and HA refers to fulvic acid