Effect of Manure Compost on Distribution of Cu and Zn in Rhizosphere Soil and Heavy Metal Accumulation by Brassica juncea

Manure compost has emerged as a method of soil amendment for phytoremediation of polluted soil by heavy metals. Pot experiments were carried out to study the effects of different dosages of manure compost (0, 20, 40, 60, 80 and 100 g/kg compost to soil) on the distribution of Cu and Zn in the rhizosphere soil and the accumulation of them by Brassica juncea during the phytoremediation process. The rhizosphere soil and plant tissues were sampled at 42 days after planting to determine the concentration of heavy metals in the samples by using flame atomic absorption spectroscopy. pH value, electrical conductivity, and nutrients (alkaline-N, olsen-P, and olsen-K) increased with the addition of compost. The percentages of exchangeable Cu and residual Cu decreased, while the proportion of other fractions increased with increasing amount of manure compost. The fractions of exchangeable Zn, Fe-Mn oxide-bound Zn, and residual Zn have the same variation tendency as Cu. The variation tendencies of exchangeable Zn, Fe-Mn oxide-bound Zn, and residual Zn are the same as that of Cu. Concentrations of Cu and Zn in the overground and underground parts of B. juncea had a significant increase up to a maximum at 60 g/kg compost and then decreased. Bioaccumulation coefficients reached maximum values of 1.44 and 1.35 in the overground and underground parts of B. juncea at 60 g/kg compost, respectively. The biomass of B. juncea and total metal accumulation in B. juncea increased to the maximum at 60 g/kg compost. Obtained results indicated that appropriate amount of soil amendment is very important aspects for phytoremediation of heavy metal-contaminated soil.