Effects of pH on toxicity of Cadmium towards
soil microbial biomass in the presence of organic acids was studied. The results
showed that: in the soils contaminated by Cadmium, the
microbial biomass C and N increased with enhancement of soil pH at a given concentration of organic acids, but the ratio of
soil microbial biomass C:N decreased with increase of soil pH. The boosted rate was faster in the soils receiving humic acid than that adding low molecular weight organic acids (oxalic acid, acetic acid, citric acid, tartaric acid ), suggesting that increased soil pH decrease the toxicity of Cadmium towards soil microbial biomass. In addition, the values of microbial biomass C and N in the soil added with low molecular weight organic acids were lower than those without addition of organic acids at soil pH<6.0. But the values of microbial biomass C and N in the soil containing humic acid were higher than those without addition of organic acids in all pH range. It meant that low molecular weight organic acids could increase the toxicity of Cadmium at lower pH range and humic acid could decrease the toxicity of Cadmium in soil.