The total soil Cu was determined by flame Atomic Absorption Spectrometry before test start. Soil samples were first digested in a heating block using 5 ml of a 70% concentrated HNO3 solution in 100 mg dry soil. Temperature was increased from 80◦ C up to 110◦C until all fluid from the samples became clear and the acid was evaporated. Before AAS analysis the samples were dissolved in 0.1 M HCl