| Soil contamination by heavy metals has threatened the safety of agricultural products and become one of the major obstacles restricting the sustainable development of society.It is very urgent to seek effective methods to remove heavy metals from soils.Soil washing can quickly remove heavy metals from contaminated soil.Previous studies have mainly focused on the removal rate of heavy metal and the effect on physicochemical properties by washing,while ignored the safety of agricultural soil utilization after washing.In this study,we focused on the combined effect of soil washing(MC)and chemical amendments(inorganic amendments,organic amendments,and their mixed amendments)to remediate the soil contaminated with multi-metals.Soil incubation experiment and pot experiment were conducted to investigate that effect of different amendments on physicochemical properties and the distribution of heavy metal fractions during incubation time,and biomass of maize,heavy metal concentrations of maize in alkaline and acidic washed soil.The study results showed that:(1)The results of batch experiment showed that inorganic amendment(calcium carbonnate,zeolite)decreased the concentration of available Cd and Zn,While organic amendments,particularly chicken manure,were more effective to decrease Pb availability in washed soil.The combined amendment of 0.2% calcium carbonate and 2% chicken manure was more effective to reduce Cd,Pb,Cu and Zn availability by 45.78%,75.92%,9.35%and 14.95%,respectively,compared with the control treatment.Besides,the combination amendments could not only enhanced the fertility of washed soil but significantly increased shoot growth of Chinese cabbage.(2)The results of the washing experiment showed that the removal efficiencies were 72.26%,50.83%,28.06%,and 27.46% in alkaline soil and41.91%,28.75%,28.05%,and 13.88% in acid soil for Cd,Pb,Cu and Zn.Theresults of incubation experiment showed that amendments increased the contents of organic matter,CEC,available phosphorus,available potassium,total nitrogen,total phosphorus and total potassium in the two kinds of washed soils,and the physicochemical properties tended to be stable with the incubation time.With calcium hydroxide+chicken manure application in the alkaline and acid washed soil,compared with the control treatment after 180 days incubation,organic matter increased 25.31% and 13.64%,CEC increased 9.14% and 1.03 times,available phosphorus increased 2.18 times and 22.37%,available potassium increased 3.15 times and 19.49 times,total phosphorus increased 5.92 times and 10.73%,respectively,compared with the control treatment.(3)The results of incubation experiments on metal speciation showed as follows: compared with the control treatment,calcium hydroxide+chicken manure significantly reduced the concentrations of available and unstable Pb and Cu in alkaline washed soil by 1.85% and 8.75%,6.05% and 8.32%,respectively,and the reduction trendency was stable and sustainable for a certain time,but less affected on Cd and Zn.For the acid soil,chicken manure and calcium hydroxide+chicken manure significantly reduced the concentrations of unstable Pb,Cu,Zn.After 180 days incubation,this above amendments decreased these metals by 4.95%,9.15%,6.95% and 4.16%,9.03%,7.53%,respectively,and the reduction trendency was stable and sustainable for a certain time.(4)The pot experiment showed that chicken manure,calcium hydroxide+chicken manure significantly increased the biomass of the above ground part of maize in the alkaline and acid washed soil by 27.22%,29.06%and 103.12%,62.23%,respectively.For the alkaline washed soil,chicken manure,calcium hydroxide+chicken,and biochar+chicken manure decreased effectively Cu in the above ground part of maize by 15.44%,15.44%,22.00%,respectively.For the acid soil,calcium hydroxide+chicken had the best effect to decrease Cd,Pb,Cu,and Zn in the above ground part of maize by 89.74%,52.86%,57.73% and 60.16%.Amendments could reduced bioconcentration factor of Cd,Pb,Cu,and Zn in maize in the acid washed soils. |
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