NITRIFICATION PROCESS AS AN INDICATOR OF SOIL CONTAMINATION WITH HEAVY METALS

The effect of soil contamination with heavy metals on the nitrification process was determined in a laboratory experiment. The study involved samples of typical brown soil with a granulometric composition of loamy sand, collected from the arable and humus horizon. The experiment was performed in three replications. Soil samples were contaminated with the following amounts of nickel chloride, copper chloride and zinc chloride: 0, 100, 300, 600 mg Me kg(-1) soil. Nitrogen was supplied in the form of ammonium sulfate at a dose of 0, 250 mg N kg(-1) soil. The pollutants were thoroughly mixed with the samples, and soil moisture content was brought to 50 % capillary water capacity. Samples were incubated in a thermostat at a temperature of 25 degrees C for 42 days. N-NH4+ and N-NO3- levels in the soil were determined on experimental days 1, 14, 28 and 42. Soil contamination with heavy metals (Ni2+, Cu2+, Zn2+) significantly reduced the rate of nitrification. On the 42nd day of the experiment, the tested metals inhibited nitrification by 1 % to 15 % when the administered dose was 100 mg kg(-1) soil, and by 14 % to 40 % when the pollutant dose reached 300 mg kg(-1) soil. The highest level of contamination at 600 mg kg(-1) inhibited nitrification by 70 % to 72 %. The process was most adversely affected by nickel, it was less influenced by copper, while zinc had the least effect on nitrification. A close correlation between the nitrification process and the degree and type of soil pollution with heavy metals renders nitrification rate a highly objective parameter in the evaluation of soil contamination.