The concentration of Fe in B. vulgaris was higher in control plants than in the cow manure and olive husk treatments. The levels of Fe were higher in plants cultivated with inorganic fertiliser, although the control and olive husk plots had greater Fe availability ( Table 2). The excess of available Mn in the soil with olive husk treatment may have caused antagonism between Fe and Mn with respect to plant uptake ( Kabata-Pendias, 2001). Elevated Mn concentrations in plants were found in all treatments; according to Jones et al. (1991), Mn concentrations greater than 60 mg kg−1 can be considered high in plants. The Mn/Fe ratio increased from control (1.05) to manure (1.62) and olive husk treatment (2.34), a symptom of increasing Mn toxicity ( Poschenrieder and Barceló, 1981). Hue et al. (2001) reported Mn phytotoxicity in soybean plants grown in soils amended with manure and biosolids, as a consequence of the appearance of a strong reducing environment. Copper concentrations in B. vulgaris were lower than the toxic values (20 mg kg−1; Kabata-Pendias, 2001). However, the levels of Zn found in the olive husk-treated plants can be considered toxic (100–400 mg kg−1; Kabata-Pendias, 2001).