Effects of the Combined Pollution of Lead and Cadmium on Soil Urease Activity and Nitrification

The effects of heavy metals contamination on soil are quite alarming and can cause huge disturbances in the ecological balance and health of living creatures on earth. Effects of the heavy metals combined pollution of lead (Pb2+) and cadmium (Cd2+) cations on soil urease activity and nitrification were studied by soil incubation method to evaluate whether there is a synergistic interaction on soil enzyme activities, nutrient cycling and pollutants. Results showed that activated effect on soil urease activity was found only in the low concentrations (such as 0.5 mg/kg Pb2+ and 0.5 mg/kg Cd2+ combined) than the control, and the inhibitory effect was existed in most of the higher concentrations (P < 0.05). With the increasing of Pb2+ concentration in soil from 0.5 mg/kg to 100.0 mg/kg combined with 0.5 mg/kg of Cd2+, the soil urease activity decreased and varied as the incubation proceeded. At the same time, soil nitrification was also inhibited in a certain degree with the threat of heavy metals contamination, and the nitrifying activity in contaminated soil samples were significantly lower than the control. A statistical analysis indicated that there were some correlations between the inhibition of soil urease activities and nitrification.