The study of Chinese humic acid was started in the late 1950s, mainly from the use of peat. In the 1960s, the national craze of using humic acid fertilizer and improved soil promoted the comprehensive development and utilization of humic acid in China.
According to source, humic acid can be divided into natural humic acid and artificial humic acid. In the natural humic acid, it is divided into soil humic acid, coal humic acid, water humic acid and mould humic acid.
According to the generation method, humic acid can be divided into original humic acid and regenerated humic acid (including humic acid in natural weathered coal and artificial oxidized coal).
According to the solubility and color classification in solvents, humic acid can be divided into yellow humic acid, brown humic acid and black rot acid. In the previous literature, there were also the names of ash, brown, and green humic acid, which were separated by different solvents.
According to the natural union state, it is divided into free humic acid and (calcium and magnesium) combined with humic acid.
According to the degree of corrosion of humic acid (the index of absorption coefficient and so on), it is divided into type A, type B (real humic acid) and RP type and p-type (immature humic acid).
Although the classification of humic acid is varied, it has little effect on our research and application.