Advanced techniques for characterization of organic matter from anaerobically digested grapemarc distillery effluents and amended soils

The effects of grapemarc distillery effluents on the quality of soil organic matter is extremely important to ensure the environmentally-safe and agronomically efficient use of these materials as organic amendment. In this work, the effects of the application of untreated (UG) and anaerobically digested grapemarc distillery effluents, either added with (AGM) or without mycorrhiza (AG), on soil humic acid (HA) were investigated in field plot experiments in comparison to HAs from a control soil and an inorganic fertilized soil. The humic acid-like fractions (HALs) isolated from UG, AG and soils were characterized for compositional, structural and functional properties by the use of elemental and functional group analysis, and ultraviolet/visible, Fourier transform infrared and fluorescence spectroscopies. Results obtained indicated that anaerobic digestion of effluents produced an extended mineralization with loss of organic C and stabilization of residual organic matter by increasing the content of HALs in the effluent. With respect to control soil HA, HALs isolated from UG and AG were characterized by smaller acidic functional group contents, a prevalent aliphatic character and smaller aromatic polycondensation and humification degrees. The chemical and spectroscopic characteristics of native soil HA were not substantially modified by application of UG, AG and AGM to soil, which suggests the occurred incorporation of the effluent HAL into native soil HA. In conclusion, these results showed the possibility of a beneficial and safe recycling of grapemarc distillery effluents as soil amendment.