Humic acid is not a specifically defined chemical substance, but is “a complex mixture of many different acids containing carboxyl and phenolate groups so that the mixture behaves functionally as a dibasic acid or, occasionally, as a tribasic acid” (en.Wikipedia.org). The physiochemical properties of humic acid will be determined by the substance (soil, peat, coal and various dystrophic water sources) from which it has been extracted and the procedure(s) used for extraction and purification. In order to standardize humic acid products, it would be desirable to have an infrared spectrum of each hunic acid product that would identify its component structure. Such an identification of structure could then be correlated with a particular plant response when a humic acid product is an ingredient in a nutrient solution formulation or nutrient supplement product. Humic acid, being a mixture of many molecules and having both carboxylate and phenolate groups, will form complexes with ions, such as Mg2+, Ca2+, Fe2+ and Fe3+; therefore will act in much the same way as a chelate, regulating the bio-availability of these and other ions in solution. Such chelation can have both advantages and disadvantages depending on the physiochemical characteristics of rooting media and the plant nutrient ions chelated. This role of humic acid when added to a rooting medium as a component in a nutrient solution formulation and/or supplement needs to be known in order to match the characteristics of the humic acid product with expected plant response. There is a substantial body of research relating humic acid with plant response in the soil chemistry literature than can provide guidance for its use in other types of rooting medium.
