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The effects of chicken manure on the immobilization and bioavailability of cadmium in the soil-rice system

ABSTRACT Soil cadmium (Cd) contamination has become a serious environmental concern worldwide. We conducted a two-year field experiment to investigate the effect of chicken manure as a soil amendment for the in situ immobilization of Cd, by assessing Cd bioavailability, fractions, and its uptake by rice plants. Results showed that soil pH and DTPA-extractable Cd were significantly elevated and reduced, respectively, with increasing doses of chicken. Sequential soil extractions indicated that chicken manure converted Cd to more immobilized fractions by significantly decreasing the exchangeable Cd fraction and increasing the carbonate-, oxide-, and organic matter-bound fractions. Accordingly, chicken manure significantly reduced the concentrations of Cd in rice tissues, including the brown rice (by up to 77.8%; the Cd content was below the recommended tolerable limits of 0.2 mg kg−1); such effects did not vary much in the 2 years. In this study, chicken manure could effectively reduce the bio-availability of Cd as it increased the soil pH, decrease the content of DTPA-extractable Cd, and transformed Cd into more stable fractions; as a result, chicken manure can be used as an amendment to significantly reduce Cd concentrations in rice if the heavy metal input through its application is considered in a long run.