Effects Of Different Phosphate Fertilizers On Lead And Cadmium Availability And Bioaccumulation In Tea Garden Soil

The pollution of lead (Pb) and cadmium (Cd) in tea garden soils and tea leaves is more and more serious and method using phosphorus to repair heavy metal contaminated soil is increasingly developed. Based on former studies, we put phosphorus use into the tea garden soil and tea plant system for in-situ remediation to study the effects of different phosphate fertilizers and application rates on Pb and Cd contaminated tea garden soil, thus to provide scientific basis for reasonable phosphate fertilizer application and to ensure quality of tea plants safety in Pb and Cd contaminated tea garden soil. A pot experiment was conducted to evaluate the effects of phosphate fertilizers with application rates of 0.2 and 0.5g P2O5·kg-1 on soil pH, bioavailable Pb and Cd and absorption and accumulation by tea plants in different culture period (after 1,2 and 4 months cultivation). The main results of this research are as follows:(1) The increase of soil pH under calcium superphosphate (CSP) and monobasic kalium phosphate (MKP) treatment was not obvious; while application of calcium magnesium phosphate (CMP) significantly increased soil pH, and as the application rate increased the soil pH increased. This showed that CMP could effectively improve the acid environment of tea garden soil.(2) Compared with CK, all treatments improved bioavailable Pb (HCl extracted state) content in different extents among which CMP increased bioavailable Pb most significantly and as the application rate of CMP increased the bioavailable Pb content increased. CMP and CSP increased bioavailable Cd (HCl extracted state) content significantly; after 4 months treatment, bioavailable Cd content of MKP was lower than CK, while the decreasing range was small.(3) The accumulation of Pb in tea root showed clear and that of Cd showed very strong; the enrichment capacity of Pb and Cd in tissues of the tea plant followed the order of root>stem>leaf; most Pb and Cd accumulated in the root organ, the Bioaccumulation Factor (BAF) of leaf was no more than 1, thus showed weak enrichment capacity in tea leaf.(4) CMP at higher application rate significantly reduced Pb and Cd absorption in all tissues of the tea plant; Pb and Cd absorption in all tissues of the tea plant at higher application rate were lower than those at lower application rate; all treatments at lower application rate made Pb absorption increase in root, CSP and CMP increased Pb absorption in leaf, while the effect of MKP was insignificant compared with CK; after 4 months treatment, CMP and MKP made Cd absorption decrease in root and all phosphate fertilizers at lower application rate made Cd absorption increase in leaf.(5) Under our experimental conditions, the correlation between soil pH and bioavailable Pb and Cd showed positive way, while the correlation between soil pH and Pb and Cd absorption in tea plants was negative; bioavailable Pb was not related to Pb absorption in tea plants, while bioavailable Cd was negatively related to Cd absorption in tea plants; there was close correlation among Pb and Cd absorption in tissues of tea plants.