Bioactivity of humic acids isolated from vermicomposts at different maturation stages

Vermicomposts are useful to improve environmental quality and sustainable agriculture. Moreover, it is enriched with highly bioactive humic acids (HAs)-like substances and can substitute no-renew source of humic substances to use as plant growth promoters in agriculture. The aim of this work was to evaluate the biological effects of HAs isolated at increasing vermicompost maturation stages. Lateral root emergence, aqueous growth medium acidification and proton pumps of maize seedlings were used to monitor HAs bioactivity. Molecular conformation of the HAs was determined by size-exclusion and reverse-phase high performance liquid chromatography. We applied spectroscopy C-13-NMR on VC samples to follow the humification process. We observed a decrease of carbohydrate content and selective preservation of hydrophobic alkyl and aryl C components by C-13-NMR during vermicompost maturation. Apparent molecular weight distribution of HAs did not change with vermicompost maturation, but was possible observed increase on hydrophobic moieties. After 60 days of vermicomposting, all HAs promotes lateral root emergence, acidification of growth aqueous medium and induction of proton pumps without changes on apparent molecular weight but with enhance on hydrophobic domains.