EFFECTS OF HEAVY METALS (Cd, Zn and Cu) ON CARBON, NITROGEN AND IRON MINERALIZATION IN SOIL

Abstract

A sixty days laboratory incubation study was conducted to investigate the effect of heavy metals on soil carbon,

nitrogen and iron mineralization under aerobic condition. Sulphate salts of cadmium, zinc and copper were added

individually and in combinations to soil samples and incubated in different plastic pots. Soil organic carbon did not

change significantly throughout the incubation period. Soil microbial biomass carbon declined from 0.38mgkg-1to

0.19 mgkg-1 in Cd treated soil and 0.39 mgkg-1 to 0.28 mgkg-1 in Cu treated soil which account for about 50% and

28% reduction (p ≤0.05) in biomass carbon respectively. Cd:Zn and Cu:Cd treated soil had reduced 36.84% while

Zn:Cu had 42.11% reduction in biomass carbon.CO2-C effluxes peaked by day 15 for all the single metal amended

soil indicating that priming effects might have occurred. But in combination, metal showed some interaction for

what the respiration rates were declined for the first 15 days. Rapid ammonification with presumed immobilization

took place up to day 30. The result indicated a significant (p ≤0.05) net mineralization of nitrogen for Cd:Zn

(63.72%) and Cu:Cd (66.66%) treatments at the end of the experiment. Available iron content showed significant

changes in combined metal treatment than a single metal.