The presence of soluble phenolic compounds in the olive husk (Table 1) could help to solubilise Cu by chelation, as observed by the increase in DTPA-extractable Cu in the first two samplings; these functional groups are known to easily chelate Cu2+ (Borges et al., 2005). Later, as the degradation of the organic compounds occurred during the experiment, the differences in extractable-Cu were not statistically significant among treatments.