EN
Experiments were performed in the greenhouse of the University of Warmia and Mazury in Olsztyn, on soil taken from A-horizon. Under natural conditions it was leached brown soil developed from light loamy sand with pHKCl 5.8 and pHKCl 6.3. The tested metal was applied in the form of ZnCl2 or ZnS04 7H20, at the following doses: 0, 400, 800, 1,200, 1,600 mg Zn2+ kg-1 d.m. of soil (experiment 1); 0, 200, 400, 600, 800, 1,200, 1,600 mgZn+ kg-1 d.m. of soil (experiment 2). Prior to the establishment of the experiments, soil samples were mixed with mineral fertilizers and, in some treatments, with pine sawdust or finely ground barley straw in the amount of 0 and 5 g kg-1 d.m. of soil. Excessive zinc accumulation in soils modified the counts oligotrophic bacteria and copiotrophic bacteria. The effect of this metal was related not only to its dose and type of chemical compound, but also to crop species and organic fertilization.