Limed sewage sludge effects on nutrient status and metal fractions in acidic soils

The potential impacts of limed sludge on nutrient and heavy metal bioavaila bility must be studied for their safe use on acidic soils. The objective of this study was to assess the impact of limed sludges on six acidic soils f rom eastern Canada. CaCO3 and raw sewage sludges (RSS) stabilized with eith er CaO (CaO + S) or cement kiln dust (CKD + S) were added to soils in amoun t necessary to reach pH 6.5 and the mixtures were then incubated for 64 d. CaO + S treatments were the most efficient to neutralize soil acidity. Afte r 10 d of incubation, the Sr-citrate extractable P was significantly increa sed by the CaO + S treatment in low P sorption soils. The extractable K, Zn and Cu contents were also slightly increased by CaO + S compared to CaCO3 whereas CKD + S resulted in an excessive soil exchangeable K content. After 64 d, labile Al content was decreased by all liming amendments. RSS and Ca O + S tended to increase labile Cu and Mn contents. The RSS increased NaOH- extractable Cu but the treatments had no significant effects on the labile and stable forms of heavy metals. A combination of CaO+CKD to stabilize sew age sludge would be more suitable to provide appropriate levels of P and K without resulting in large increases in extractable heavy metal contents.