Effects Of Different Amendments On Heavy Metals Chemical Speciations Transformation And Plant Absorption In Calcareous Soil

The problem of heavy metal pollution in soil is becoming more and more serious.Although the environmental capacity of heavy metals in slightly alkaline soil is often higher than that of acidic soil,some heavy metals in north China calcareous soil could difficult to be utilized by plants,but could exceed the environmental capacity and cause serious environmental damage.Moreover,heavy metals could be absorbed by plants and it could accumulate in the plant,animal and human body through the food chain,which is a serious threat to human health.Therefore,the heavy metal pollution needs to be remedied urgently.The combination study of pot experiment and field experiment was carried out in calcareous soils with two different pollution degree,and the soil used in pot experiment had heavier pollution than the field experiment soil.In this study,Pot experiments planted chicory and maize,and applied biochar,bentonite,lignite and the combination of them,chicory was growed for 60 days and was harvested,and maize for 30 days and was harvested.For investigating the change of soil pH,the change of chemical speciation transformation of Cd,Pb,Ni,Cu and Zn in soil,the characteristics of plant growth and absorption of heavy metals after application of amendments;the field experiment was applied with biochar,chicken manure and lignite as amendments,investigating the varieties of soil pH,the varieties of Cd,Pb,Ni,Cu and Zn in soil and the absorption of heavy metals in various organs of wheat under different growth period.Furthermore,some amendment materials and their combinations suitable for alleviating heavy metal pollution in calcareous soil in north China was selected.The main findings are as follows:The results of pot experiment:(1)Different amendments had different effects on soil pH because of their different properties.Biochar could increase soil pH value,bentonite had no significant effect on soil pH,and lignite could decrease soil pH value.The dose at the 4%addition level had significant effect,and the application effect of only one amendment was better than that of the combination.(2)The amendments had significant effect on Cd,Pb,Ni,Cu and Zn.After adding amendments,the proportion of exchangeable heavy metals among 5 kinds of chemical speciations decreased in varying extent,and promoted their transformation to forms that were not easily absorbed and utilized by plants.Among different treatments,the 4%addition level of lgnite had significant effect on Cd and Cu forms in pot experiment.(3)The combination of bentonite and lignite at 4%addition level had the greatest increase in plant height of chicory;The compound of biochar and bentonite at 4%addition level had the significantly increase in plant biomass of chicory.The combination of bentonite and lignite at 4%addition level could maximized maize plant height and biomass among different treatments.(4)The amendments had a certain immobilization effect on the absorption of heavy metals by chicory and maize.The combination of bentonite and lignite at 4%addition level could significantly reduce the absorption of Cd,Pb and Cu in stem,leaf and root of chicory;The 4%addition level of lgnite could significantly reduce the absorption of Ni and Zn in chicory stem,leaf and root.The 4%addition level of lignite significantly restrained the absorption of Cd by maize stem,leaf and root.The combination of biochar and lignite at 4%addition level restrained the absorption of Pb,Cu and Zn by maize stems,leafs and roots.The 4%addition level of biochar significantly restrained absorption of Ni by maize stem,leaf and root.However,the amendments had a weak immobilization effect on heavy metal transport.The results of wheat field experiment:(1)After the amendments were applied,the soil pH value had been changed.The biochar increased the soil pH value,the lignite and chicken manure deceased the pH value,but the effect of biochar and lignite is not obvious.The 2%addition level of chicken manure could significantly decrease soil pH value by 0.20 units.(2)In the field experiment,the 2% addition level of lignite significantly decreased the exchangeable form of Cd and Pb,the carbonate bound form of Ni at every growth stage,and the 2%addition level of biochar significantly decreased the exchangeable form of Cu and Zn at every growth stage and increased the residual form of Cu and the organic binding form of Zn.(3)The 1% addition level of lignite could significantly decrease the Cd content in wheat grains by 56.47%.The 2%addition level of lignite could significantly decrease the Pb content in wheat grain,with a decline of 25.11%.The 2%addition level of chicken manure could significantly decrease the content of Ni in wheat grain by 46.48%.The 2%addition level of biochar could significantly decrease the content of Cu and Zn in wheat grain,which declined by 18.19%and 23.56%.Overall,biochar and lignite had better effects than that of chicken manure.The paper systematically studied the effects of different amendments on heavy metals chemical speciations transformation and plant absorption in calcareous soil.Pot experiment and field experiment had different degree of heavy metal contamination,and amendments had differences in chemical,mineral,physical and biological properties.However,the addition of amendments had immobilization effect on heavy metals to some extent,and transform the chemical forms of heavy metals from high to low availability.What's more,amendments decreased the bioavailability of heavy metals and decreased the absorption and utilization of plants.Lignite had a significant effect on different degrees of pollution.