Influence of organic material addition on the variation of Cd activity in submerged soils

A red soil (pH 4.46) and a fluvo-aquic soil (pH 7.10) were submerged and incubated under nitrogen coverage for 60 days with the addition of clover and straw in order to elucidate the controlling mechanism on Cd activity in flooded soils. The reductive dissolution of iron oxides resulted in the decline of pe+pH and Fe redistribution in solid phase, which led to the Cd transformation to low activity fractions. Following the flooding and organic material (OM) addition, Cd activity were strongly affected by the decrease of pe+pH and the variation of pH in soils. For the red soil treated with OM, the decline of pe+pH and the rise of pH caused the Exc-Cd and soluble Cd lower than control (CK). In contrast, in fluvo-aquic soil, OM addition caused the Exc-Cd and soluble Cd higher than CK as a result of the simultaneous decrease of pe+pH and pH. For both soils, OM addition had only minor influence on the Org-Cd in solid phase. However, dissolved organic matter (DOM) enhanced the Cd complexation in soil solution.