humic acid

one of two classes of natural acidic organic polymer that can be extracted from humus found in soil, sediment, or aquatic environments. The process by which humic acid forms in humus is not well understood, but the consensus is that it accumulates gradually as a residue from the metabolism of microorganisms. Humic acid is the humic fraction soluble in alkali, but not in acid. The other organic polymer is fulvic acid.