Humic substances are carbon-rich materials formed primarily through microbial decomposition of dead plant matter, a process called humification, carried out by bacteria and fungi. These substances are found in soils, compost, peats, water, and various types of coals, which differ based on the conditions of peat formation, such as vegetation, climate, and geological processes. Because of these variations, humic substances from different sources have distinct properties and effects on plants.

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