Copper, zinc, iron and manganese contents were determined in edible parts of some fresh vegetables sold on markets in Poznañ. The copper and zinc contents in vegetables obtained in the present study were compared to the ones reported from an analogous study carried out in the Department of Horticultural Plant Fertilization in Poznañ fifteen years ago. Samples of vegetables were collected from six points distributed in the area of Poznañ from March to July at monthly intervals. For the study, vegetables were divided into three groups according to edible parts: leaves (lettuce, cabbage, parsley, leek), roots (carrot, celeriac, parsley) and fruits (tomato, cucumber). The concentration of copper, zinc, iron and manganese was determined by the atomic flame absorption method using an AAS 3 Zeiss apparatus. The highest content of copper was found in roots of celeriac, while the smallest content was shown in cabbage leaves. The highest mean content of zinc was found in lettuce leaves and the lowest one in tomato fruit. The mean content of copper in all the vegetable species was lower in 2005 than in 1993. In 1993 more zinc was found in vegetables whose edible parts were fruits compared to the results of 2005. The vegetables whose leaves and roots are eaten were characterized by a higher zinc content in 2005. The highest content of iron was found in leaves of leek, while the lowest amounts were determined in tomato and cucumber fruits. The highest mean content of manganese was found in leaves of lettuce, while the smallest amount was in carrot roots. The iron content in the vegetables whose leaves and fruits are edible parts was lower in 2005 than in 1993, while the root vegetables were characterized by more iron in 2005. Higher content of manganese in all the vegetable species examined was found in 1993 than in 2005.

In 2007-2008, pot experiments were conducted on cv. Michalina head lettuce grown in an unheated greenhouse in spring. The aim of the study was to compare organic and mineral iron compounds as well as their rates in terms of the efficiency of their effect on yield of lettuce and iron content in lettuce leaves. The experimental factors included: 1) sources of iron, i.e. 2 mineral-iron(II) sulfate and iron (III) sulfate, and 3 organic-iron (III) citrate, iron (II) gluconate and iron chelate Fe (III) DTPA, 2) level of iron, i.e. 6 levels-20 (control), 45, 70, 95, 120 and 220 mg Fe dm-3 substrate. Lettuce was grown in 6 dm 3 containers. Limed highmoor peat, enriched with macroand micronutrients to meet requirements of lettuce, was used as a substrate. Each experiment included 26 combinations comprising 4 replications each. A container with 4 lettuce plants constituted one replication. Lettuce was harvested at the consumption stage. Concentrations of iron, copper, manganese and zinc were determined in plant material by ASA after wet mineralization in a mixture of acids HNO 3 and HClO 4 at a 3:1 ratio (v:v). The application of iron(III) sulfate, iron(II) sulfate, iron citrate or iron gluconate ranging from 45 to 220 mg Fe dm-3 and Librel Fe-DTPA chelate ranging from 45 to 120 mg Fe dm-3 did not have any significant effect on the yield of lettuce. Librel Fe-DTPA applied at a rate of 220 mg Fe dm-3 resulted in a reduction of yield. The highest Fe content (irrespectively of the applied Fe rates) in lettuce leaves was recorded after the application of Librel Fe DTPA, while the lowest one-after iron gluconate was used. When analyzing the effect of Fe levels, irrespectively of the used iron compounds, the lowest Fe content in leaves was observed in the control, growing at the levels of 45 and 70 mg Fe dm-3 , as well as at 90 and 120 mg Fe dm-3 and reaching its peak after the application of 220 mg Fe dm-3 .