Definition of terms related to humic acid

(1) Soil organic matter. Refers to all natural organic matter present in the soil, including non-humus (fresh, incompletely decomposed animal and plant residues) and humus (including humic and non-humic substances).

(2) Humic substances. Refers to a class of heterogeneous aliphatic-aromatic amorphous organic polymer mixtures rich in multiple active functional groups, formed by the humification process of animal and plant residues, mainly plant residues, decomposed and synthesized by microorganisms (some continue to change through geophysical and chemical effects). According to the solubility in different solvents, humic substances can be divided into humic acid (humic acid), palmitic acid (gemadomelanic acid), fulvic acid (fulvic acid) and humin (humin).

(3) Humus. A class of high molecular complex mixtures decomposed and synthesized by microorganisms in soil organic matter, including: ① Humic matter: products after humification (with fatty and aromatic properties, polydisperse organic electrolyte properties); ② Non-humic matter: other strong decomposition and microbial metabolites after non-humification (including proteins, amino acids, carbohydrates, waxes, resins, fats, tannins, lignin and its decomposition products, etc.).

(4) Fulvic acid. Components in humic matter that are soluble in alkaline, acidic, neutral aqueous solutions and acetone and ethanol (the original meaning was the part of soluble organic acid that remains in the acidic solution after alkali dissolution and acid precipitation of coal organic matter. In recent years, the soil science community has greatly expanded the scope of the concept of "fulvic acid").

(5) Humic acid. In soil science, it refers to the fraction extracted from humic matter with alkaline solution and precipitated with acid (including black humic acid and brown humic acid). In many literature materials and daily habits, the term "humic acid" is often used as an abbreviation for "humic acid substances", which actually also includes fulvic acid. In some humic acid chemical analysis methods, in order to simplify the operation procedures, the components soluble in alkaline solution are often called humic acid (including fulvic acid). Readers should pay attention to distinguish when reading.

(6) Hymatomelanic acid. The fraction of humic acid that is soluble in polar organic solvents such as acetone and ethanol. This fraction can generally only be extracted from the humic acid colloid obtained by alkaline dissolution and acid precipitation.

(7) Pyrotomalenic acid. It is called "true humic acid" in Russian literature, which refers to the humic acid component that is only soluble in alkaline solution and insoluble in water, acidic solution, acetone and ethanol, that is, the part of humic acid left after the palmitic acid is extracted from the humic acid colloid.

(8) Humin. It is also called "humin" in soil science, "residual coal" in coal chemistry, and "asphaltene" in Russian literature, that is, the neutral condensed aromatic macromolecular humic matter left after humic acid is extracted with alkaline solution.

(9) Bonded humic acid. Humic acid with active functional groups bonded to high-valent metal ions (Ca2+, Mg2+, Fe3+, etc.) is commonly known as "high calcium magnesium humic acid" in my country. It is difficult to dissolve in alkaline solution and can only be extracted with sodium pyrophosphate alkaline solution.

(10) Free humic acid. Humic acid with active functional groups bonded to H+ is humic matter that can be extracted with alkaline solution.

(11) Total humic acid. The general term for bound humic acid and free humic acid.

(12) Humates. The product of the reaction of humic acid with various metal ions or ammonium ions, including monovalent humic acid salts (potassium humate, sodium humate, ammonium humate) and multivalent salts (common ones are calcium humate, magnesium humate, iron humate, zinc phytate, etc.). In fact, humic acid salts generally contain fulvic acid.

(13) Humic acid summations. The sum of humic acid, palmitic acid and black humic acid contents (used for quantitative analysis of humic acid).