What is Humic acid and its Effect on Soil

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What is humic substance:

Humic substance is a mixture of exceedingly complex organic molecules that lack structural regularity.

Where humic acid substances are found:

They are found in soil, sediments and natural water .They present organic matter in peat bogs, carbonaceous shales and brown coals.

Classical fractions of humus:

Humic acid:

The fraction of humic substances not soluble in water at pH values lower than 2 but soluble at higher pH values. It is dark brown to black in color.

Fulvic acid:

The fraction of humic substances is soluble in water under all pH condition. It change color on all pH. At low pH they are straw yellow color. At pH 3 its color is orange and wine red at high pH.

Humin:

The fraction of humic substances not soluble in water at any pH value.

Effect of humic acid on soil:

Humic acid enhances soil nutrient availability and soil water holding capacity. What is humic substance:

Humic substance is a mixture of exceedingly complex organic molecules that lack structural regularity.

Where humic acid substances are found:

They are found in soil, sediments and natural water .They present organic matter in peat bogs, carbonaceous shales and brown coals.

Classical fractions of humus:

Humic acid:

The fraction of humic substances not soluble in water at pH values lower than 2 but soluble at higher pH values. It is dark brown to black in color.

Fulvic acid:

The fraction of humic substances is soluble in water under all pH condition. It change color on all pH. At low pH they are straw yellow color. At pH 3 its color is orange and wine red at high pH.

Humin:

The fraction of humic substances not soluble in water at any pH value.

Effect of humic acid on soil:

Humic acid enhances soil nutrient availability and soil water holding capacity. Therefore, humic acid extracted from pulverized weathered coal was suitable to apply in the field since it decreased the ammonia (NH3) volatilization and carbon dioxide (CO2) emission. In addition, humic acid significantly decreased water evaporation and enhanced water use efficiency by plants in low clay content and water holding capacity soils (e.g., sandy and arid soils).

Humic acid significantly improved soil macroaggregates and could efficiently reduce soil salinity (M. Liu et al., 2019). By boosting up the cohesive forces of very fine soil particles(<0.002 mm), humatereduced soil erosion (Khaled & Fawy,2011).

Humic acid could affect the soil microbe community; for instance, fungal and bacterial community structures in the different growth stages were enhanced soil critical nutrient level and plant nutrient sufficiency range (M. Liu et al., 2019), where humic acid promoted nutrient chelate and made nutrients available to plants (Khaled & Fawy, 2011).

Furthermore, humic acid had the potential to act as a washing agent for the soil’s toxic elements, including arsenic (As), cadmium (Cd), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) in the in- or ex-situ remediation mechanism (Mosa et al., 2021). Biochar-humic acid wood vinegar acted as a radiation material to immobilize nickel (Ni) metal in soil effectively (Zhu et al., 2021). In addition, the role of wood vinegar was to increase the oxygen-containing group (Zhu et al., 2021).  In short, humic acid can improve soil properties and microbial activity and remediate contaminated soil.