"Humic substances are the naturally occurring biogenic, heterogeneous organic compounds resulting from the decomposition of plant, animal and microbial residues, over many thousands of years. Research into humic substances have found them to be beneficial not only for crop production, but for human and animal health also. Humic substances influence crop yields by affecting soil texture, water retention, nutrient buffering capacity and microbial diversity. Their stimulatory effects on plant growth and physiology can be ascribed to enhanced nutrient uptake, hormonal activity with root growth and proliferation, activation of antioxidant defense under various abiotic stresses. Furthermore, their potential to remove toxic pollutants from soil as well as aquatic systems might resolve the problem of degrading environment."
https://www.intechopen.com/chapters/78385
"Humic acid is a naturally available organic acid in soil that promotes the growth and yield of crop plants by improving their nutrient status. Humic acids are largely available from lignite or coal mines and many agriculture companies sell it as growth-promoting substances."
https://link.springer.com/chapter/10.1007/978-3-031-09943-4_6
"Organic matter and humus have been a study focus of many scientists and researchers since at least the 18th century. At the present time, it is recognized that humus influences soil fertility through its effect on the water-holding capacity of the soil.
According to Ohio State University study, "humic acids increased plant growth" and there were "relatively large responses at low application rates”."
https://www.ahi-intl.farm/post/benefits-of-humic-acid-in-modern-agriculture
"Humic acids (HA) are organic molecules that play essential roles in improving soil properties, plant growth, and agronomic parameters. The sources of HA include coal, lignite, soils, and organic materials. Humic acid-based products have been used in crop production in recent years to ensure the sustainability of agriculture production."
https://www.frontiersin.org/articles/10.3389/fagro.2022.848621/full
"Humic acid is a group of molecules that bind to, and help plant roots receive, water and nutrients. High humic acid levels can dramatically increase yields. Humic acid deficiency can prevent farmers and gardeners from growing crops with optimum nutrition."
https://www.ecofarmingdaily.com/build-soil/humus/humic-acid/
Humic Acid
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/humic-acid