The original large molecular clusters of mineral source humic acid have a high degree of aggregation, poor water solubility, and their active sites are encapsulated. When directly mixed into fertilizers, their agronomic effects are limited. After activation modification, the molecular chains break and the proportion of small molecule components increases. The carboxyl groups, phenolic hydroxyl groups, etc. of the active groups are exposed. When combined with compound fertilizers, slow-release fertilizers, and water-soluble fertilizers, they can exert synergistic and additive effects in five dimensions: nutrient regulation, soil improvement, root stimulation, stress resistance enhancement, and heavy metal detoxification. They are important functional components for reducing fertilizer use and increasing efficiency, as well as for conserving cultivated land.

1. Regulate nutrient transformation and improve fertilizer utilization rate

Activated humic acid has dual characteristics of colloid adsorption and complexation, which can stabilize and regulate nitrogen, phosphorus, potassium, and trace elements.

For nitrogen: By inhibiting urease activity and adsorbing ammonium nitrogen, it reduces ammonia volatilization and nitrate leaching loss, and prolongs the nitrogen supply period. Liu Yanli et al. in a wheat-corn rotation field experiment showed that when activated humic acid was combined with urea, the nitrogen fertilizer recovery rate in the current season was 37% to 93% higher than that of single application of urea, and wheat yield increased by 15% to 28%, and corn yield increased by 8% to 10%.

For phosphorus: Activated humic acid can form complexes with calcium, iron, and aluminum ions in the soil, reducing the fixation of phosphate ions, activating the potential phosphorus pool in the soil, and improving the effectiveness of phosphate fertilizers, promoting the translocation of phosphorus to the above-ground parts of crops. For potassium and trace elements: It can adsorb potassium ions to reduce soil lattice fixation; at the same time, as a chelating agent, it converts iron, zinc, copper, manganese, etc. trace elements into stable chelated forms, reducing the constraints of environmental factors such as soil pH and calcium carbonate on the effectiveness of trace elements, and alleviating problems such as iron deficiency and chlorosis, and small leaf symptoms in alkaline soil.

2. Improve soil physical and chemical properties and biological characteristics, and promote the formation of macropore structures

Activated humic acid is a hydrophilic colloid. When applied to the soil, it can act as a binding substance, promoting the formation of stable aggregates, reducing soil bulk density, improving porosity, water retention, and fertilizer retention capacity, and alleviating problems such as compaction, acidification, and secondary salinization caused by long-term single application of fertilizers. At the same time, it provides carbon sources for beneficial microorganisms such as soil bacteria and actinomycetes, enhancing soil enzyme activity and microbial abundance, improving the rhizosphere microecology, and reducing the pressure of re-sowing obstacles. Wang Yuanqi et al. reviewed that the modification and activation technology of humic acid is the key means to enhance the soil improvement ability of humic acid, and the activation products have significantly better effects on soil organic carbon retention and salt buffering than unmodified raw humic acid.

3. Biological stimulation effect, promoting root growth and strengthening root absorption capacity

The small molecule components of activated humic acid have the attributes of plant biological stimulants, which can induce the upregulation of H⁺-ATPase activity in the cell membrane of roots, regulate endogenous hormone signals in the roots, promote the occurrence of lateral roots and root hairs, increase the absorption surface area of the roots; promote seed germination, shorten the recovery period after seedling emergence, and alleviate stunted seedlings and weak seedlings. The review by the Institute of Agricultural Science and Technology of the Chinese Academy of Agricultural Sciences indicated that the root-promoting effect of humic acid mainly comes from the low-molecular-weight, high-carboxyl content activated components, and not from the large-molecular crude humic acid, which is also the core value of the activation process. 。

4. Enhance crop's stress resistance, stabilize yield and improve agricultural product quality

The activation of humic acid can regulate the plant's antioxidant system, increase the content of osmotic regulatory substances such as proline and soluble proteins, and enhance the crop's ability to resist drought, tolerate low temperatures, withstand saline-alkali conditions, and alleviate fertilizer damage; at the same time, it can increase the chlorophyll content and photosynthetic rate of leaves, promote the transportation of photosynthetic products to fruits and seeds, reduce nitrate accumulation in fruits, increase soluble sugar and vitamin content, improve fruit shape, color and taste, and achieve stable yield and quality improvement. Xu Hongnan et al. proved in an apple orchard that the activated humic acid slow-release fertilizer significantly improved the SPAD and photosynthetic indicators of leaves, and increased apple yield by 31.64% to 41.70%.

5. Reduce heavy metal toxicity, lower the risk of heavy metal migration to agricultural products

The abundant carboxyl and phenolic hydroxyl groups on the surface of activated humic acid can combine with heavy metal ions such as cadmium, lead, copper and zinc through complexation, ion exchange and surface adsorption, reducing the effective content of heavy metals and inhibiting the transfer of heavy metals from soil to crop roots. It has application value in safe utilization of cultivated land and green agricultural product production.

Adding activated humic acid as a functional carrier to the fertilizer system is not a simple combination of organic materials, but utilizes the structural advantages brought by activation and modification to achieve multiple synergistic effects such as increased nutrient efficiency, soil improvement, promotion of root resistance, and risk reduction, which is in line with the direction of reducing fertilizer use, improving cultivated land quality, and promoting agricultural green development in China.