It is well known that less oxidized, higher molecular weight humic matter is more important in the process of aggregate stabilization than more oxidized humic substances of lower molecular weight. This effect could be due to an equilibrium between the adsorption of Na and the chelating of Ca and Mg by the organic anions, particularly at alkaline pH values. Piccolo and Mbagwu (1990) suggested that aggregate stability is significantly correlated with humic but not fulvic acid concentration, because the humic acids are directly involved in clay-organic complex formation, whereas fulvic acids are not. Fulvic acids are macromolecules with a lower polymerisation index than humic acids. Hence, the aggregates formed are more stable in CGCC than in PM-amended soils (Piccolo and Mbagwu, 1990; Porta et al., 1994). In addition, ESP decreased during the experimental period at the highest CGCC dose. According to Mamedov et al. (2002), this would reflect aggregability in these soils.