Copper and Zn uptake by radish and pakchoi as affected by application of livestock and poultry manures

Environmental safety of agricultural utilization of livestock and poultry manures from intensive farming is attracting great attention because the manures often contain high concentrations of heavy metals and organic pollutants. Pot experiments, in which a pig manure (PM), a chicken manure (CM) and a commercial organic manure (OM) with different concentrations of Cu and Zn to simulate soil metal accumulation by manure application for different times were utilized in a garden soil at a rate of 2% (W/W), were conducted to study the effect of application of these livestock and poultry manures on growth of radish (Raphanus sativus L.) and pakchoi (Brassica chinensis L.) as well as their Cu and Zn uptake. The results exhibit that the manures except the PM improved the growth of radish and pakchoi. The difference of biomass among the same manure treatments containing different concentrations of Cu and Zn, however, was insignificant. In addition, application of the livestock and poultry manures significantly increased soil pHs and electric conductivities (EC) compared with the control, which is ascribed that these manures had high pH and contained large amounts of inorganic ions. The available soil Zn concentrations in the PM were higher than that in the CM and OM, and the extractable soil Cu concentrations in the three manures were almost the same after radish growth in the garden soil but were different after pakchoi growth. Zinc and Cu concentrations in the radish and pakchoi tissues increased when the soil Zn and Cu concentrations increased by manures application, but were still within a safe value. An except is the treatment PM4 in which the Zn concentration of the above-ground part of radish was 28.7 mg kg−1, exceeding the Chinese Food Hygiene Standard of 20 mg kg−1 based on fresh weight. Good correlation was obtained between the extractable soil Zn (or Cu) concentrations extracted by 1.0 mol l−1 NH4NO3 and the Zn (or Cu) concentrations in radish and pakchoi tissues, which was expected to be effective in forecasting Cu and Zn availability to radish and pakchoi in manure agronomic utilization.