The differences among bio-fermented humic acid, chemically synthesized humic acid, and oxidatively regenerated humic acid.

　　From the perspective of humic acid types, the main categories are bio‑fermented humic acid, chemically synthesized humic acid, and oxidatively regenerated humic acid. Their raw material sources are extremely diverse, including crop straw, wood chips, sugar‑production residues, bagasse, brewing waste liquids, paper‑making effluents, animal manure, and various other agricultural by‑products and renewable industrial waste materials that can be fully utilized. Although “artificial humic acid” closely resembles “soil humic acid,” their stability differs significantly.

　　1. Bio-fermented humic acid

　　At present, among bio‑fermented humic acid products, those produced via fermentation to yield fulvic acid are the most commercially advanced. Fulvic acid represents the essence of humic acids. While humic acids are high‑molecular‑weight organic acids, fulvic acids are low‑molecular‑weight and highly active; consequently, fermented fulvic acid products enjoy the broadest range of applications in agriculture. Bio‑fermented humic or fulvic acids are obtained by mimicking the natural formation process of humic substances—particularly the early stages of peat humification—through inoculated fermentation.

　　Fiber-degrading microorganisms can break down lignocellulosic materials—such as carbohydrates, fibers, plant residues, and wood—to produce humic acid or fulvic acid. Certain microorganisms, including actinomycetes, Penicillium, Pseudomonas, fungi, and Aspergillus, can also synthesize humic acids through biochemical processes. For example, some researchers have used glycerol and nitrate as culture media to produce humic or fulvic acid with actinomycetes, in which more than 40% of the nitrogen is present in the form of amines and amino acids. Others have cultivated Aspergillus in a glucose-based medium and observed the formation of phenols, peptides, and amino acids, which subsequently undergo condensation to yield humic or fulvic acid.

　　2. Chemically Synthesized Humic Acid

　　Many researchers abroad have simulated the natural formation of humic acids by conducting oxidation–condensation reactions using polyphenols, various carbohydrates, urea, or lignin together with nitrogen-containing organic compounds (such as proteins). The reaction media employed include acidic or alkaline solutions and alcoholic ammonia, while catalysts comprise metal ions and iron oxides, among others.

　　3. Oxidative Regeneration of Humic Acid

　　Coal and lignocellulosic materials that do not contain humic acids can yield “regenerated humic acids” under the action of oxidizing agents (such as nitric acid, ozone, atmospheric oxygen, potassium permanganate, hydrogen peroxide, persulfates, etc.); however, the reaction conditions are quite stringent, requiring strong acids or bases, high temperatures, and elevated pressures.

　　Among the major categories within the two broad classifications—“natural humic acid” and “synthetic humic acid”—it is still “coal‑derived humic acid” that has achieved large‑scale, commercial, and product‑line‑based development and application. Within “synthetic humic acid,” the dominant sector is primarily “fermentation‑derived fulvic acid.” This indicates that both “coal‑derived humic acid” and “fermentation‑derived fulvic acid” are setting the direction for the development of humic‑acid‑based products, with very promising prospects for future growth.