Distribution of the organic matter and humic acid characteristic in soils with addition of residues of urban origin

The aim of this work was to determine potential changes in the distribution of humified fractions of the organic matter together with the structural features of humic acids in samples from the superficial horizon of two soils (Ultisol and Oxisol) to which 80 ton ha(-1) of both compost of municipal residues and sewage sludge were added. An increase in the fulvic acids content was found which implies both a decrease in the humic/fulvic acid ratio and also in the quality of the humus in the soils. The humic acids studied underwent structural changes, mainly the decrease in the long alkyl chain content along with an increase in the C content related to polysaccharides incorporated to the humic acids.