Characterization of fulvic acids by elemental and spectroscopic (FTIR and 13C-NMR) analyses during composting of olive mill wastes plus straw

Elemental, functional and spectroscopic analyses (FTIR, 13C-NMR) were performed to study fulvic acids of composted olive mill wastes plus cereal straw, in order to follow the maturity of the final product during composting. The extracted fulvic acids were characterized by high nitrogen, acidic functional group and phenolic hydroxyl contents that might have resulted from the high degree of humification and the synthesis of more condensed humic complexes. This was confirmed by a decrease of alcoholic and aliphatic structures and an increase of aromatic structures, as shown by the FTIR and 13C-NMR analyses. The results showed that stability of the final product was reached after 12 months of composting and that fulvic acid levels could constitute an additional tool to assess final product maturity and its agronomic value.