Humic acid fertilizer is a general term for various humic acid-containing fertilizers, mostly made from peat moss, lignite, etc., through specific processes of extraction, concentration, or conversion into water-soluble fertilizers containing nutrients. For example, humic acid-rich raw materials are added with sodium hydroxide to produce sodium humate; sulfuric acid is added to produce humic acid; nitric acid is added to humic acid-containing raw materials to produce nitrohumic acid; potassium hydroxide is added to produce potassium nitrohumate; or ammoniation is used to produce ammonium humate.
Humic acid is added during the production of compound fertilizers, or nutrients and humic acid are added during the production of basic fertilizers to produce humic acid compound fertilizers.
What are the advantages of humic acid fertilizer?
The synergistic effect of humic acid on fertilizers
Humic acid can adsorb, exchange, and activate many mineral elements in the soil, such as nitrogen, phosphorus, potassium, calcium, and magnesium, greatly increasing the availability of these elements and thus improving the nutritional conditions of crops. It acts as a synergist in chemical fertilizers and reduces the adverse effects of chemical fertilizers on the physical and chemical properties of the soil.
1. The Enhancing Effect of Humic Acid on Nitrogen Fertilizer
Nitrogen fertilizer is essential for plant growth. The main nitrogen fertilizers are urea and ammonium bicarbonate. When urea and ammonium bicarbonate are applied to the soil, they are quickly lost through air and water, with crops only able to absorb and utilize about 30% of the nitrogen nutrients.
The aromatic nuclei, hydroxyl groups, and carboxyl groups in humic acid can react with nitrogen to form stable new ionic groups, also called complexes. These complexes remain in the soil for a relatively long time, gradually decomposing and releasing nitrogen for plants to absorb slowly.
Statistics show that the nitrogen released from urea and ammonium bicarbonate, after complexing with humic acid, can maintain its fertilizer effect for more than 60 days, increasing nitrogen fertilizer utilization by more than 10%.
2. The Enhancing Effect of Humic Acid on Phosphate Fertilizer
After phosphate fertilizer is applied to the soil, phosphorus is fixed by metal ions in the soil, converting readily available phosphorus into slow-release phosphorus or ineffective phosphorus.
The aromatic nuclei, hydroxyl groups, and carboxyl groups in humic acid can react with phosphorus to form soluble phosphorus, increasing its activity and making it easier for plants to absorb. Statistics show that applying humic acid fertilizer can relatively increase the efficiency of phosphate fertilizer by 5%-10%.
3. The Synergistic Effect of Humic Acid on Potassium Fertilizer
The functional groups in humic acid can also absorb and store potassium ions, preventing potassium ion loss in sandy soils and potassium fixation in clay soils, thus increasing potassium fertilizer utilization by about 5%.
The Role of Humic Acid in Soil Improvement
Current scientific research shows that soil fertility largely depends on the humic acid content in the soil. A series of properties of humic acid, such as cation exchange capacity, oxygen content, and water retention capacity, are the main reasons why humic acid increases soil fertility and promotes plant growth. Most importantly, humic acid can combine with metal cations, oxygen, and hydroxides, releasing them slowly for crop utilization. Due to these properties, humic acid can exert multiple effects in soil improvement, including physical, chemical, and ecological effects. First, humic acid can improve the physical structure of soil. It promotes the formation of soil aggregates, enhances the soil’s water and fertilizer retention capacity, and improves aeration and permeability in harder soils such as saline-alkali land. This alters the soil’s high alkalinity, dispersed soil particles, and poor structure, thus improving cultivation conditions. Humic acid also has a good effect on improving alkaline soils and red soils. It can bind and bind soil surfaces to retain moisture, preventing soil cracking and erosion. Further loosening the soil increases aeration and soil utilization, enhances drought resistance, darkens the soil color, and makes it more conducive to sunlight absorption.
Second, humic acid plays the following roles in improving the chemical properties of soil. It neutralizes soil acidity and alkalinity, adjusting pH levels; it chelates metal cations to facilitate root absorption; it retains moisture at the crop roots, dissolving inorganic fertilizers and reducing their loss; it reduces the reaction of phosphorus with calcium, iron, magnesium, and aluminum, or converts them from ineffective states into forms that can be absorbed and utilized by plants; it can reduce toxic substances in the soil.
What are the methods of application?
① Base fertilizer: Apply 300-400 kg/mu of a 0.02%–0.05% humic acid aqueous solution mixed with farmyard manure, or apply as a base fertilizer by trenching or digging pits. In paddy fields, it can be applied during land preparation and irrigation.
② Topdressing: During the seedling and heading stages, apply 250 kg/mu of a 0.01%–0.1% humic acid aqueous solution, irrigating near the roots (avoiding direct contact with the roots). In paddy fields, sodium or potassium humate can be applied with irrigation water or by splashing to promote seedling growth, strong panicles, and overall growth and development.
③ Foliar spraying. From late flowering to early grain filling, apply foliar spray two or three times, each time using 50-75 kg of a 0.01%-0.05% humic acid aqueous solution per acre. This will promote plump grains, increase thousand-grain weight, and reduce empty grains. Spraying is best done between 2-6 PM.
④ Seed soaking. Soak seeds in a 0.01%-0.05% humic acid aqueous solution. Soak vegetable and wheat seeds for 5-10 hours, and rice and cotton seeds for more than 24 hours. This can improve germination rate, promote early emergence, and enhance seedling root development.
⑤ Dipping seedling roots and soaking cuttings. For transplanted crops such as rice, sweet potatoes, and vegetables, soak roots in a 0.05%-0.1% sodium humate or potassium humate solution for several hours before transplanting, or dip seedling roots when transplanting. Soak fruit tree cuttings. This promotes rapid root development, increases secondary roots, shortens the recovery period, and improves survival rate.
What should be noted when using humic acid fertilizer? 1. Pay attention to concentration.
Humic acid fertilizers work somewhat similarly to growth regulators. During use, it’s crucial to pay close attention to the concentration. If the concentration is too high or too low, the effect on crops will be minimal, and in severe cases, it may even hinder crop growth and development.
2. Pay attention to temperature.
When using humic acid fertilizers, temperature is paramount. Generally, it takes about 18 hours for the fertilizer to take effect at the optimal temperature. Using humic acid fertilizer at low temperatures will result in a very slow effect, easily leading to fertilizer waste and increased planting costs. Conversely, using it at high temperatures may cause fertilizer burn, severely impacting crop yield.
3. Pay attention to combined use.
Humic acid fertilizers are more effective as base fertilizer and seed fertilizer than as top dressing. Concentrated application is better than broadcasting, and deep application is better than shallow application. However, it’s important to note that it cannot completely replace inorganic fertilizers and farmyard manure; it must be used in combination with chemical and organic fertilizers.
Humic acid fertilizer, as a natural organic fertilizer, is increasingly widely used in modern agricultural production due to its multiple advantages such as improving soil, enhancing the efficiency of chemical fertilizers, and improving crop resistance.
