The effect of heavy metals (lead, nickel and cadmium) and cow manure on population changes of indigenous soil nematodes

Heavy metals are categorized as one of the most important contaminants that disturb soil environment and thus are harmful to terrestrial organisms. There are many ecological indices representing such pollutions. Nematodes as indicator organisms may be a suitable index to assess environmental conditions. The objective of this study was to investigate the impact of different levels of selected heavy metals (Cd, Ni, and Pb) and cow manure on nematode population changes of indigenous soil nematodes. A completely randomized design with factorial arrangement was carried out including 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 and two levels of cow manure 0 (O0) and 1% (O1) with 3 replications. Soil moisture of all treatments was adjusted at 70% of field capacity. All treatments were incubated for 30 and 90 days. Soils were then washed and the total population, juvenile and mature numbers of nematodes was determined. All isolated nematodes were identified at the family level and ecological indices (enrichment, structure and maturity) were determined. The results showed that total population, juvenile, mature numbers of nematodes decreased significantly in all metal amended treatments. Furthermore, calculated ecological indices tended to decline by addition of heavy metals into soil samples.