Molecular characteristics of humic acids isolated from vermicomposts and their relationship to bioactivity.

Vermitechnology is an effective composting method, which transforms biomass into nutrient-rich organic fertilizer. Mature vermicompost is a renewable organic product containing humic substances with high biological activity. The aim of this study was to assess the chemical characteristics and the bioactivity of humic acids isolated from different vermicomposts produced with either cattle manure, sugar cane bagasse, sunflower cake from seed oil extraction, or filter cake from a sugar cane factory. More than 200 different molecules were found, and it was possible to identify chemical markers on humic acids according to the nature of the organic source. The large hydrophobic character of humic extracts and the preservation of altered lignin derivatives confer to humic acids the ability to induce lateral root emergence in maize seedlings. Humic acid-like substances extracted from plant biomass residues represent an additional valuable product of vermicomposting that can be used as a plant growth promoter.