Humic acid improves soil structure.

Humic substances have colloidal properties. Through flocculation, they can form aggregates with soil aggregates and micro-aggregates, reducing soil bulk density and increasing porosity. This gives the soil good permeability, which helps regulate the conditions of water, fertilizer, air, and heat in the soil, creating a favorable soil environment for plant root growth and development, and ultimately increasing crop yield.

Humic acid improves saline-alkali soil.

Humic acid is a negatively charged colloid. When combined with soil, it increases the adsorption capacity for cations, playing a role in salt isolation and absorption, inhibiting the upward movement of salt, and reducing the salt content in the topsoil. Humic acid is a weak acid that can combine with various cations in the soil to form humates, creating a buffering system for the mutual conversion of humic acid and humates, which effectively regulates soil pH. Humic acid can also undergo neutralization reactions with alkaline substances in the soil, reducing soil alkalinity. The base exchange capacity of humic acid is 200–300 cmol/kg, which is 10–20 times that of clay minerals in the soil, allowing harmful ions in the soil solution to undergo exchange reactions with humic acid, thereby reducing the salt content of the soil. Therefore, humic acid plays a significant role in the improvement of saline-alkali land.

Humic acid increases soil fertility.

The functional groups in humic acid, such as carboxyl, carbonyl, alcohol hydroxyl, and phenolic hydroxyl groups, have strong ion exchange and adsorption capacities, which can reduce the loss of ammonium nitrogen and improve nitrogen fertilizer utilization. Research shows that urea is hydrolyzed to NH₃, and NH₃ is hydrated to form NH₄⁺. Due to the large internal surface area and strong adsorption capacity of humic acid, NH₄⁺ is quickly adsorbed by humic acid and undergoes ammoniation to form humic acid ammonium salts with a low degree of dissociation. These salts can provide NH₄⁺ to crops while reducing ammonia volatilization. In addition, humic acid in the soil enhances microbial activity, especially significantly increasing the population of free-living nitrogen-fixing bacteria, strengthening biological nitrogen fixation, increasing nitrate content in the soil, and providing abundant nitrogen nutrition for crops.

Humic acid promotes the degradation of organic matter by soil microorganisms.

Humic acid is an organic substance that can provide nutrients for soil microorganisms. Humic acid improves soil structure, reduces soil bulk density, increases soil porosity and permeability, regulates soil pH, and reduces soil salinity, thereby creating an excellent living environment for microorganisms, allowing them to multiply extensively and promoting the degradation of organic matter in the soil by microorganisms. At the same time, humic acid increases the activity of oxidase enzymes, accelerating the degradation rate of organic pollutants.