In pot experiments, in spring 2006 and 2007, a comparison was made between the chelated and the mineral forms of copper on the yielding of lettuce and on the content of Cu, Zn, Mn and Fe in lettuce leaves. Plants were grown in peat substrate supplemented with Cu doses of 5, 25, 50 and 75 mg∙dm^-3. A greater mass of lettuce heads was obtained after the application of the mineral form of copper. In the range of doses: 5–50 mg Cu∙dm^-3, the mean yields of lettuce did not differ. In the second year of studies, the application of copper chelates in the dose of 75 mg∙dm^-3 caused a high reduction of yield. The mean copper content in lettuce, after the application of the chelated Cu form, was twice higher than after the use of the mineral Cu form. Iron content in lettuce after the application of copper chelates was higher than after the use of copper sulphate, while the contents of zinc and manganese were smaller.

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