Heavy metals are categorized as one of the most important contaminants that disturb soil environment and thus are harmful for terrestrial organisms. Nematodes as an indicator organism may be a suitable index to assess heavy metals risks in the soil. Also, organic compounds such as manure have an important role in nematode population traits. The objective of this study was to investigate the impact of different levels of heavy metals (Cd, Ni, and Pb) and organic matter on nematode population characteristics of soil. Therefore, a completely randomized factorial design was carried out including two levels of organic matter 0 (O0) and 1% (O1) and three levels of heavy metals 0 (H0); 100, 500, 1000 (H1); and 300, 700, 2000 (H2) mg kg-1 of Cd, Ni, and Pb, respectively. All treatments were incubated for three months at 27°C and 70% of field capacity soil moisture. After 30 and 90 days incubation time, the total population, juvenile and mature numbers of nematodes were determined. The results showed that total population, juvenile and mature numbers of nematodes significantly decreased by addition of heavy metals. The results also revealed that the adverse effects of the metals may be masked by organic matter application.

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