Composition changes of soil humus after massive application of urban wastecompost: a comparison between FT-IR spectroscopy and humification parameters

A laboratory trial and a six-year field experiment were carried out to eval uate the changes in the composition of humic substances in a soil amended f or six years with urban waste compost (UWC), and to compare the results obt ained by FT-IR spectroscopy with empirical humification parameters. The ful vic acid FT-IR spectra showed that amended soils contain a higher concentra tion of carboxylic and aliphatic groups compared to unamended soil (UNAS). The six-year amended soil (SYAS) also showed a higher content of polysaccha rides on FT-IR spectra of both humic and fulvic acids. The polysaccharide i ncrease in the six-year amended soil is attributable to the humification pr ocess since polysaccharides were not present in a high quantity in the UWC or laboratory amended soil (LAAS). The humification index and the degree of humification values indicate that the urban waste compost and soils studie d can be classified in decreasing order of humification as follows: UNAS > SYAS > LAAS > UWC. This behaviour is the consequence of an increasing prese nce of the non humified fraction in NaOH extracted organic matter. The carb oxylic and aliphatic groups content from FT-IR spectra confirmed this behav iour, thus indicating the validity of the humification parameters used to e valuate the status of the organic matter from refuse and soil.