Phytoavailability of cadmium to cherry-red radish in soils applied composted chicken or pig manure

Abstract

The aim of this study was to assess phytoavailability of cadmium to crop in soils applied composted animal manures. In a greenhouse experiment cherry-red radish ( Raphanus sativus) was grown in two soils applied with different levels of Cd with chicken manure or pig manure compost, compared with those of Cd applied in metal salt. Phytoavailable Cd was determined as Cd concentration in radish leaf or root. Results indicated that phytoavailability of Cd applied through manure composts was significantly ( P < 0.001) less than the same rate of Cd amended with soluble CdCl 2 suggesting the lower potential hazard of composted manure-applied Cd. Radish leaves had higher concentrations of Cd than the roots. Phytoavailability of applied Cd in acidic Ferralsols was significantly ( P < 0.001) greater than that in Calcaric Cambisols. The risk of applied Cd from composted manures to radish was also assessed by bioconcentration factors (BCF values) and uptake coefficients (UCs). The relationships between Cd concentrations of plant and Cd loading rates could be expressed by quadratic equation and suggested that uptake of metals by radish plant become less efficient at higher Cd loadings. Sequential extraction scheme indicated that increasing rates of Cd applied through chicken or pig manure compost did not increase exchangeable fraction of Cd, but mainly increase its inorganic precipitated and residual fractions. The precipitated and/or residual fraction of Cd combined with soil pH could explain significantly 95% or 92% of the variation in phytoavailable Cd expressed as Cd content in radish leaves or roots when chicken manure compost was applied, and 88% or 84% of the variation in phytoavailable Cd when pig manure compost was applied. However, for soluble CdCl 2 amendment, the phytoavailable Cd in radish leaves or roots could be explained significantly (89% or 92%) by exchangeable Cd and soil pH. The results of this experiment point to the fact that the Cd source, loading rate, soil pH, and plant tissue are important factors in evaluation of Cd phytoavailability. Results also demonstrated the importance of solid-phase Cd fractions, EDTA fraction and/or HNO 3 fraction, in predicting phytoavailability of Cd in soils applied manure compost.