Humic acids (HA) are mainly functional acid groups such as phenolic or carboxylic groups. In fact, they can be extracted by reagents such as strong bases, neutral salts, chelates or organic solvents and are insoluble in dilute acids.

They are products of polymerization or condensation of the fulvic acids (FA) themselves and other decomposing products. Its molecules have a weight between 20,000 and 1,360,000 D.

Fulvic acids, on the other hand, contain basic functional groups that in fact precipitate with diluted acid. They are considered product of the decomposition of upper plant residues and microbial residues, with molecular weights between 275 to 2110 D.