The objective of this study was to evaluate the nitrification rate in soil polluted with zinc. The experimental protocol was as follows: soil (sandy loam) collected from the 0-20 cm layer of a cropped field was passed through a 2 mm mesh sieve, placed in 150 cm3 glass beakers, 100 g of soil in each, and polluted with the following doses of Zn2+ per 1 kg d.m. of soil: 0, 300, 600, 1 200 and 2 400. Zinc was applied in the form of ZnCl2 aqueous solution. Afterwards, ammonia nitrogen as (NH4)2SO4 was The objective of this study was to evaluate the nitrification rate in soil polluted with zinc. The experimental protocol was as follows: soil (sandy loam) collected from the 0-20 cm layer of a cropped field was passed through a 2 mm mesh sieve, placed in 150 cm3 glass beakers, 100 g of soil in each, and polluted with the following doses of Zn2+ per 1 kg d.m. of soil: 0, 300, 600, 1200 and 2400. Zinc was applied in the form of ZnCl2 aqueous solution. Afterwards, ammonia nitrogen as (NH4)2SO4 was added to the soil material in two doses: 0 and 240 mg N kg-1 d.m. Once zinc chloride and ammonium sulphate had been thoroughly mixed with the soil, water was added until the soil moisture content reached 50% of capillary water holding capacity and then the beakers were placed in a laboratory incubator at 25ºC. After 10, 20, 30 and 40 days, the incubated soil was tested to determine the content of N-NH4 and N-NH3. Additionally, after 10 and 40 days of incubation, the most probable counts of nitrifying bacteria involved in the first and second step of the nitrification process were determined. The experiment was run with three replicates for each day. Two determinations of each parameter were performed in the soil samples placed in beakers. In total, 6 results were obtained for each experimental variant. Based on the determinations, the amounts of nitrified and immobilized nitrogen were calculated and the resistance (RS) and resilience (RL) of the nitrification process and nitrifying bacteria to the contamination of soil with zinc were expressed. It has been experimentally demonstrated that excess zinc in soil significantly disturbs the nitrification rate. As little as 300 mg Zn2+ kg-1 d.m. of soil significantly inhibits nitrification. Zinc contamination interferes with nitrification and other metabolic process which affect soil nitrogen, which is confirmed by depressed nitrogen immobilization at higher rates of soil contamination with this element.The adverse effect of zinc on nitrification is primarily due to the negative impact of this element in the soil environment on nitrifying bacteria. Zinc more strongly inhibits the first than the second step nitrification bacteria, but ammonia-oxidizing bacteria recover more quickly than nitrate forms. The RS parameters for the nitrification process towards zinc pollution were on a low level and tended to decrease as the degree of zinc contamination rose. The resistance of nitrifying bacteria to zinc decreased parallel to the increasing amounts of zinc in soil.

19.2.2014