As a soil conditioner, humic acid has an obvious regulatory effect on nutrient forms in the soil. The main functions can be summarized as follows:
(1) Humic acid can compete with phosphate for adsorption sites on the surface of soil minerals and reduce the adsorption of phosphate by soil minerals.
(2) Humic acid can combine with calcium ions in the soil and interact with Ca-P, reducing the formation of Ca-P precipitation and improving the effectiveness of phosphorus in soil and fertilizers.
(3) Studies have shown that humic acid has the ability to bind potassium ions in the soil and enhance its resistance to soil adsorption, so it has the function of improving soil potassium availability and preventing fixation.
(4) Because it has more acidic groups, the application of humic acid can reduce the soil pH value, thereby increasing the effectiveness of trace elements (Zn, Mn, Fe, Cu) in the soil.