SENSITIVITY OF SOIL UREASE TO SOIL CONTAMINATION BY ZINC, COPPER, NICKEL, CADMIUM AND LEAD

The research objective has been to determine relationships between the activity of urease, its resistance and soil contamination with Zn2+, Cu2+, Ni2+, Cd2+ and Pb2+ in an experimental set up on loamy sand, sandy loam and sandy clay loam of pH values 5.5 and 7.0. The research comprised laboratory experiments. Soil (loamy sand, sandy loam and sandy clay loam) was polluted with the above metals and, on days 30, 60 and 120 of incubation, it was submitted to determination of the activity of urease. The results were used to calculate the resistance index (RS) of urease to contamination by heavy metals. The experimental results proved that the highest urease activity persisted in sandy clay loam and the lowest one appeared in loamy sand. The heavy metals significantly inhibited urease. The most severe inhibition of urease was caused by Zn2+ and Cu2+, less so by Ni2+ and Cd2+, while Pb2+ was responsible for the weakest urease inhibition. Strict correlation was found between the resistance of urease and the level of soil contamination by heavy metals. The highest resistance was demonstrated by urease in Cd-polluted sandy clay loam at pH 7.0, where the RS index ranged from 0.698 to 0.931. The lowest values of the RS index were observed in the same type of soil polluted by Zn2+ (RS from 0.823 to 0.016), Cu2+ (RS from 0.404 to 0.070) and Ni2+ (RS from 0.810 to 0.040).