Activation and Storage of Soil Nutrients by Humus Substances
The nutrients required by plants are continuously accumulated and supplied through the process of fixation and mineralization of soil humus substances. N, P, S can exist in the complex organic polymer and humus substance structure of soil, while alkaline nutrients, such as inorganic cations Ca, Mg, K exist on the surface of soil organic matter, and trace elements such as Mn, Cu, Fe, Zn exist in the form of organic complexes.
The storage and release of nutrients are generally carried out through two types of basic processes - N, P, S are mainly biological processes, and trace element cations are mainly physicochemical processes.
It has been proved that soil with humic acid application for many years can also release a considerable amount of P, S and other cationic elements in the soil, even without the simultaneous application of the chemical and micronutrient fertilizers, due to the activation of the immobilized elements by the humus substances. Therefore, it can be believed that the storage, activation and effectiveness of humic acid on soil nutrients are positively correlated with the amount of humic acid added.