Microbial biomass carbon is a standard technique
used to determine the effect of toxic substances on
the soil microbial community (Chander and Brookes,
1993; Diaz Ravina et al., 1994).The results in Table 6
show that the lowest measurement were obtained from
the Cu:Zn and Cu amendments. The biomass
measurement of Cu:Zn amendment was lower than the
recorded values for either individual metals. Other
authors (Chander and Brookes,1993; Kelly and
Tate,1998)reported similar results, with respect to Zn
and Cu and concluded that an additive effect was
responsible for the enhanced effect noticed in the
relationship between the metallic species in their report.
It can be inferred therefore, that additive effect and not