A spectroscopic study on soil fulvic acids composition after six-year applications of urban waste compost

A FT-IR, 1H- and 13C-NMR study was carried out to determine the changes in the composition of fulvic acids (FA) in a soil that was repeatedly amended with urban waste compost (UWC). Fuloic acids were extracted from a clay-loam soil (unamended soil - UNS), a compost and two soil-compost mixtures. One soil sample was taken from a freshly prepared laboratory mixture (LAS) while the other was collected from a 6-year field experiment 8 months after the last amendment (6YAS). Spectroscopic analyses of fuloic acids extracted from compost and unamended soil showed that the former had a higher content of aliphatic and carboxylic groups and a lower content of carbohydrates and aromatic C. Immediately after compost addition, soil fuloic acids had a higher content of aliphatic C-H and carboxylic groups and a lower content of aromatic rings and polysaccharides. The results showed that there was a progressive modification of soil organic matter during the six-year field experiment. Although the concentration of aliphatic chains, aromatic rings and polysaccharides tended to return to the value of the unamended control, a greater variety in functional groups was observed by the spectroscopic analysis.