Humic Acid in Soil

Sources

• The decay and transformation of biological materials from organisms, primarily plants, is the main source for humic acid in the soil. This process is called humification. Lignin from plants and the things it turns into as it decays -- such as polysaccharides, melanin, cutin, proteins, lipids, nucleic acids and fine char particles -- are all vital to the makeup of humic acids.

Actions

• Humic acid is involved in weathering soil materials particularly in the fine particle fraction. The amount of humic acid in the soil is also affected by pH buffering. The mobility of trace metals and their level of toxicity in the soil are changed by the amount of humic acid in the soil. Having more humic acid in the soil will make a soil safer if it has been exposed to toxins, such as lead or arsenic.

Extraction

• Humic acid can be extracted from the soil for measurement and analysis with a dilute alkali or other reagents, which is then precipitated with acid until a pH of 1 or 2 is reached. By extracting humic acid from the soil, information about the fertility and water-holding capacity of a particular soil can be determined. This provides information for understanding details about a soil.

Reactivity

• The chemical reactivity of humic acid is high. However, humic acid is extremely resistant to biodegradation. The specific extent of the different properties of a humic acid will depend on properties of the soil it was extracted from.