How much do you know about humic acid?

Everyone says humic acid fertilizers are great—so just how good are they, and what makes them so beneficial? And how can they be used most effectively? Below, we’ll provide a detailed overview.

Research indicates that, compared with the use of conventional chemical fertilizers, applying humic acid fertilizers and organic–inorganic compound fertilizers typically increases yields of field crops such as grains and oilseeds by approximately 8% to 20%, while boosting the production of cash crops like melons, fruits, and vegetables by roughly 15% to 35%. Due to their unique benefits, humic acid fertilizers are widely regarded in the industry as “four‑fold agents”: A slow-release agent for nitrogen fertilizers, an efficiency enhancer for phosphate fertilizers, a protective agent for potash fertilizers, and a chelating agent for secondary and micronutrients.

Humic acid The functions are divided into Three Three aspects, namely physical, chemical, and biological processes.

1. The physical effects are primarily manifested as follows: improving soil structure; preventing soil cracking and erosion; increasing soil water-holding capacity and enhancing cold resistance; and darkening soil color, thereby promoting the absorption of solar energy.

2. The chemical effects are primarily manifested as follows: regulating soil pH; improving and optimizing plant uptake of nutrients and water; enhancing soil buffering capacity; acting as a natural chelating agent under alkaline conditions (chelating metal ions to facilitate their absorption by plants); enriching the soil with organic matter and essential minerals required for plant growth; increasing the solubility of organic fertilizers and reducing nutrient losses; converting nutrients into forms readily available to plants; enhancing nitrogen uptake while reducing phosphorus fixation; immobilizing nitrogen, phosphorus, and potassium deep in the soil and retaining them within the soil profile; and accelerating the uptake of nutrients by plants, thereby improving the efficacy of inorganic fertilizers.

3. The biological effects are primarily manifested as: stimulating the growth and reproduction of beneficial soil microorganisms; and enhancing plants’ natural resistance to diseases and pests.

Humic acid three The integrated effects of these functions are manifested in the following five aspects:

1. Humic acid It is an organic colloidal substance with water-absorbing and water-retaining properties.

Humic acid has a high cation exchange capacity, strong adsorption‑buffering properties, and chelating ability, which can enhance nutrient use efficiency in the soil and mitigate the adverse effects of acidity and alkalinity.

Humic acid is an organic macromolecular colloid with strong water‑absorbing and water‑retention capabilities. While clay particles typically have a water absorption capacity of 50%–60%, humic substances can absorb 500%–600% of their own weight in water. Therefore, applying humic‑acid‑based fertilizers helps improve soil moisture conditions.

2. Humic acid It can improve soil structure.

Soil fertility is determined by the organic–inorganic complex. Inorganic mineral colloids typically account for more than 95% of the soil and exert a significant influence on its basic nutrient supply; moreover, they cannot be altered through artificial means. Organic colloids, namely humic substances, generally comprise only about 5% of the organic–inorganic complex, yet they play a role of equal importance to that of mineral colloids and can be regulated via human intervention. Applying organic fertilizers, using humic‑acid‑based soil conditioners and soil‑improving fertilizers, and increasing the content of humic acids in the soil are effective strategies.

Applying humic acid acts as a binding agent that promotes the formation of soil aggregate structures, enhancing the organic–inorganic complexation in the soil and increasing the proportion of large‑size, water‑stable aggregates, thereby improving soil structure. Consequently, the use of humic‑acid‑based fertilizers can effectively ameliorate the physical properties of various soils; for this reason, humic acid is regarded as a high‑quality soil conditioner.

3. Foliar spray application Humic acid , which can reduce stomatal conductance and decrease water transpiration and loss.

Wheat foliar application of humic acid Experiments show that The stomatal conductance of wheat leaves decreased by 33.7% compared with the control. According to research conducted by the Henan Academy of Agricultural Sciences, foliar application of humic acid not only reduces stomatal conductance but also narrows the stomatal aperture and promotes stomatal closure, while simultaneously supplying essential nutrients to the wheat plants.

4. Humic acid It can stimulate root growth in crops and enhance the roots’ water‑absorbing capacity.

Humic acid contains a variety of chemically and biologically active functional groups, which stimulate crop growth and development. It promotes earlier seed germination, emergence, flowering, and fruit set, while also increasing root length, root biomass, and root vitality, thereby enhancing the roots’ ability to absorb nutrients and water.

5. Humic acid It can enhance the plant’s intrinsic physiological regulatory functions and improve the crop’s cold tolerance.

Applying humic acid fertilizers can enhance enzyme activity in both the soil and plant tissues, regulate crop physiological metabolism, and improve crops’ tolerance to adverse environmental conditions.

How to select and make good use of it Humic acid Fertilizer?

First, select a humic acid fertilizer based on the application method. For flush application, drip irrigation, or foliar spraying, it is recommended to use potassium humate, ammonium humate, or potassium fulvate and ammonium fulvate. When applying as a base fertilizer, choose fertilizers such as ammonium humate or nitro‑ammonium humate; be sure to incorporate them into the soil, as ammonium humate is a compound of humic acid and ammonium bicarbonate that tends to volatilize. Therefore, it is not advisable for flush application or foliar spray. Additionally, do not apply sodium humate in soils with high pH (such as saline‑alkali soils).

Secondly, select humic acid fertilizers based on crop preferences and growth stages. Taking fruit trees as an example, in autumn the focus is on phosphorus and potassium fertilizers; in early spring, nitrogen fertilizer is prioritized; during bud break and differentiation, phosphorus and potassium are emphasized; and during the fruit‑expansion stage, nitrogen, potassium, calcium, and micronutrients should be applied. In addition, fertilization should be tailored to each crop’s specific needs. For instance, fruit trees, solanaceous vegetables, tobacco, and sugarcane are potassium‑loving crops, for which potassium humate fertilizer delivers the best results.

Finally, select humic acid fertilizers based on crop type and cost. Humic acid fertilizers are classified according to the types and amounts of nutrients they contain into single-element humic acid fertilizers, compound (mixed) humic acid fertilizers, organic humic acid fertilizers, organic–inorganic compound fertilizers containing humic acid, and humic acid–micronutrient fertilizers, among others.

For field crops, it is recommended to choose humic acid compound (mixed) fertilizers, which are easy to use and offer excellent value for money. For vegetables and fruit trees, you can opt for humic acid organic fertilizers, humic acid organic–inorganic compound fertilizers, or humic acid micronutrient fertilizers; these products contain 20%–45% organic matter, effectively enhancing the taste and color of the crops.

If used for flush application or foliar spray, it is recommended to choose water-soluble fertilizers containing humic acid or fulvic acid. Although these fertilizers are more expensive, they deliver rapid results and excellent performance, making them particularly suitable for high-value crops. an economic crop. Although humic acid can be applied throughout the entire growth cycle of the crop, for economic reasons it is advisable to apply it by flushing 1–2 times during four critical stages: after transplanting, before flowering, during fruit enlargement, and at the color‑change stage. Combining foliar sprays with these applications during the enlargement and color‑change phases will yield even better results.