Exploiting the Natural Resource - Lignite Humic Acid in Agriculture - A Review

Humic acid typically contains heterocyclic compounds with carboxylic, phenolic, alcoholic and carbonyl fractions extracted from lignite with high molecular weight. Humic acid has been extracted from various sources such as lignite, peat, coal, farmyard manure, coirpith besides natural persistence in soil. Humic acid plays a vital role in enhancing the nutrient uptake of crop by acting as a chelate in mobilizing nutrients. Prevents losses of degradation and leaching of nutrients and thus reduces the use of inorganic fertilizers besides increasing the efficiency of the applied fertilizers. Presence of growth promoting substances such as auxins and gibberellins had been reported in humic acid and it plays an important role in enhancing the enzymatic activities of the plants. The resistance in the plants found to be increased by the humic acid application. The soil fertility would be improved by mobilising the unavailable form of nutrients to the available form. The humic acid application at optimal rates has been reported to enhance the yield of various crops.