Humic acid is the smallest molecule and most active component in humic substances, representing the essence of these substances. In practical agricultural applications, humic acid exhibits the most stable effects, particularly with yellow humic acid showing optimal stability. Yellow humic acid is the core component of soil humus, a water-soluble aromatic organic substance with a small molecular weight generated from the decomposition and recombination of organic matter. It is the best component of humic substances in soil and is essential for forming soil aggregates.
- Enhancing the effectiveness of nitrogen fertilizer:
The active groups in yellow humic acid, including carboxyl, hydroxyl, and certain groups containing P, O, N, and S, readily form coordination compounds or chelates with various electron acceptors (such as multivalent metal ions, organic groups, or ions). For instance, compounds like humic acid-urea are chelates, reducing the loss of ammonium nitrogen and increasing the efficiency of nitrogen fertilizer. Oxidized and degraded nitro-humic acid can inhibit urease activity, reducing urea volatilization.
Addition of yellow humic acid to carbon ammonium reduces nitrogen loss from 13.1% to 2.04% over 6 days. In field trials, the efficiency of carbon ammonium fertilizer can be sustained for over 20 days, while the efficiency of yellow humic acid ammonium can last for over 60 days. Adding yellow humic acid, especially nitro-humic acid, to urea can form urea chelates, slowing down urea decomposition, reducing losses, and increasing urea utilization by about 30%, with an additional increase in delayed effectiveness by over 15%. Nitrogen utilization rate increased from 30.1% to 34.1% after adding yellow humic acid, with nitrogen uptake increasing by 10%.
The combined effect of yellow humic acid and nitrogen on plant growth and development is significant. When nitrogen and yellow humic acid are abundant, plants can synthesize more proteins, promoting cell division and growth, resulting in rapid leaf expansion and increased photosynthetic activity, thus promoting robust plant growth.
- Enhancing the effectiveness of phosphorus fertilizer:
Degraded nitro-humic acid can increase the mobility of phosphorus in the soil, inhibit the fixation of water-soluble phosphorus in the soil, convert ineffective phosphorus into effective phosphorus, and promote root absorption of phosphorus. Utilizing yellow humic acid to protect water-soluble phosphate fertilizers or phosphorus-based compound fertilizers reduces phosphorus fixation, promotes phosphorus absorption, and improves phosphorus fertilizer utilization. Efficiency trials have shown that adding 10-20% yellow humic acid to superphosphate, heavy superphosphate, or ammonium phosphate can increase efficiency by 10-20%, with phosphorus uptake increasing by 28-39%. Phosphorus fertilizer utilization increased from 15.4% to 19.3% when yellow humic acid was added, representing a relative increase in phosphorus fertilizer utilization of one-fourth.
Yellow humic acid, in combination with phosphorus fertilizer, participates in various processes within plants, including photosynthesis, respiration, energy storage and transfer, cell division, and cell enlargement.
- Enhancing the effectiveness of potassium fertilizer:
The acidic functional groups of yellow humic acid can absorb and store potassium ions, reducing potassium loss in sandy soil and highly leached soils. Yellow humic acid can prevent sticky soil from fixing potassium, increasing the exchangeable potassium content. It also has a dissolving effect on potassium-containing minerals, slowly releasing potassium and increasing the soil’s available potassium content. Utilizing its biological activity, yellow humic acid stimulates and regulates crop physiological processes, increasing potassium uptake by over 30%.
- Promoting the absorption of micronutrients, effectively addressing deficiency symptoms:
Yellow humic acid forms highly mobile chelates with micronutrients, facilitating their absorption by crops and effectively addressing deficiency symptoms.
In addition to major elements like nitrogen, phosphorus, and potassium, crop growth and development require micronutrients such as iron, boron, manganese, zinc, molybdenum, and copper. These micronutrients are essential components of various enzymes in plants and significantly influence normal growth, disease resistance, yield increase, and quality improvement. Most of the micronutrients in soil are in an ineffective state that plants find difficult to absorb, and applying micronutrient fertilizers to the soil can easily lead to their fixation.
Studies have shown that yellow humic acid can chelate with iron, zinc, and other micronutrients, forming soluble and readily absorbable chelates, such as yellow humic acid-zinc, yellow humic acid-manganese, and yellow humic acid-iron. These chelates facilitate root or foliar absorption and promote the transfer of micronutrients from roots to above-ground parts.
Experiments have shown that the quantity of iron entering plants from yellow humic acid through roots is 32% more than that from ferrous sulfate, and the quantity transported in leaves is twice as much as that from ferrous sulfate, resulting in a 15-45% increase in chlorophyll content, effectively addressing leaf yellowing caused by iron deficiency.