Morphological Distribution Of Heavy Metals In Sewage Irrigated Soils And Their Crop Response In Taiyuan Xiaodian District

The field experiment located in sewage irrigation area in Xiaodian district, Taiyuan, Shanxi province, was conducted to study systematically the content and vertical distribution feature of different form of Pb, Cr and Cd in lm soil layer, the absorption and transferring characteristics of corn, wheat and soybean on Pb, Cr and Cd, the bioavailability of different forms of heavy metals on three kinds crop, crops yield and physiological basis. In order to provide a theoretical basis for remediation and utilization of sewage irrigation soil.The main results as follows:1.The content of total Pb, Cr and Pb in soil of this study was about1to4times than the environmental background value in Taiyuan, but no more than the secondary standard of Soil Environmental Quality Standard(GB15618-1995), which could meet the general farmland standard. The content of total and Tessier extractable Pb, Cr and Pb gradually decreased with increasing soil depth, and mainly concentrated in the0-20cm soil layer, with a surface accumulation. Planting corn, wheat and soybeans had no effects on heavy meatal distribution.2.In sewage irrigated, the most speciation of soil Pb was residual form, which accounted for45.7%of the total. Pb. The second is the organic combination state, accounting for32%. The different fractionation of Pb was in an order of succession:residue> bound to organic matter>bound to Fe-Mn oxide> bound to carbonate, exchangeable; The most speciation of soil Cr was also residual form, which accounted for73.3%, then bound to Fe-Mn oxide, accounting for10.7%. The species distribution of Cr for residue> bound to Fe-Mn oxide> bound to organic matter> bound to carbonate, exchangeable; while the proportion of Cd in the residual fraction is low, only accounts for0.3%, the bound to organic matter Cd and bound Fe-Mn oxide Cd, respectively accounted for30.7%and27%, The distribution of different Cd forms in an order of succession:bound to organic matter, bound to Fe-Mn oxide> bound to carbonate, exchangeable> residue.3.The Pb, Cr and Cd enrichment mount in different parts of corn, wheat and soybean being root> stem, the leaf> grain, and the difference reached significant level (P<0.01). The enrichment coefficient in roots was the highest and was the lowest in grain. The absorption and transfer efficiency on heavy metals Pb, Cr and Cd of wheat in three crops was the lowest. The Cd metastasis rate was the highest, the Cr metastasis rate was the lowest among three kinds of heavy metals.4.The Cd content in corn, soybean seed have exceeded the standard limitation value (GB15201-94, Cd<0.05mg/kg), the over standard rates were56%and84%. The Pb, Cr contents were respectively0.97mg/kg and0.36mg/kg in soybean seed, and are close to the standard limit value (GB14961-94, Cr<lmg/kg; GB14935-94, Pb<0.4mg/kg). The exchangeable, bound to carbonate Pb and Cr in sewage irrigated soil, as well as the exchangeable Cd, bound to carbonate Cd and bound to Fe-Mn oxide has high bioavailability, which has a high contribution rate to crop seed.5.The corn, wheat and soybean yield in sewage irrigated area was significantly higher than the average yield in clean water irrigation area in the same year.The maize photosynthesis and dry matterforming ability was higher than that of wheat and soybean.The resistance of corn and soybean is higher than that of wheat.