Remediation Of Lead And Cadmium Contaminated Soil Using Lime,Humic Acid And Lolium Perenne L.

Soil is an important component of the ecosystem and the material basis for human beings and other organisms to survive.In recent years,with the rapid development of industry and agriculture,especially the exploitation of mineral resources,irrigation of agricultural sewage,and large-scale application of pesticides and fertilizers,causing soil heavy metal pollution has become increasingly severe.Therefore,taking safe and effective measures to repair soil heavy metal pollution is an urgent environmental problem.The application of soil conditioner to repair heavy metal pollution has attracted many attentions and researches in soil remediation due to its advantages such as simple operation,low input cost and obvious application effect.In this study,ryegrass(Lolium perenne L.)was taken as the experimental material,and the indoor pot experiment was conducted with 8 treatment.To explore the effects of lime,humic acid and their combined on the accumulation of Pb and Cd in ryegrass,the bioavailability and forms of heavy metals in soil,and the physiological and biochemical of ryegrass.Meanwhile,the dynamic change of soil physical and chemical properties and soil microbial activity in the remediation process of contaminated soil were analyzed.The main results are as follows:(1)The soil bioavailable Pb and Cd content was significantly reduced by the application of lime and lime combined with humic acid,and the effect of lime combined with humic acid on soil Pb bioavailability was better than that of application of single lime,especially lime + 5% humic acid better than other treatments,which was average of about 89.30% lower than that of the control.The content of acid-soluble Pb and Cd in all treatment was significantly reduced,which the effect of lime + 5% humic acid was the best,Pb and Cd were lower than control about 59.42% and 46.02%,respectively.In the late period of time(60 d),The Pb and Cd absorption in the aboveground of ryegrass was significantly decreased by the lime,humic acid and their combined.(2)In the late culture period(60 d),the soil basic respiration and soil microbial biomass carbon could be improved by the application of lime,humic acid and their combined,which the mixture of lime and humic acid was the best.During the whole culture time,FDA hydrolase activity could be increased by the application of single humic acid,soil urease and catalase activity could be increased by the application of single lime and lime combine with humic acid.(3)The Eh value of lime,humic acid and their combined was lower than that in the control.Except for the application of single humic acid,all other treatments could significantly increase soil pH,and the bioavailable Pb and Cd content was significantly negatively correlated with soil pH.During the whole period,SOC and TN in the lime,humic acid and their combined was significantly increased,which the effect of lime + 5% humic acid was the best,better than control about 98.03% and 16.91%,respectively.(4)The biomass of the aboveground and underground part of ryegrass could be significantly improved,which lime + 2% humic acid(T6)and lime + 5% humic acid(T7)better than control about 59.71% and 41.47%,respectively.SOD activity was significantly increased,POD activity and malondialdehyde content was reduced in all treatments.(5)It indicated that the effect of lime combined with humic acid on the bioavailability of Pb and Cd in farmland soil was different from that the application of single lime or humic acid.There was an obvious interaction between the mixture of lime and humic acid,whose efficiency controlling on soil Pb and Cd bioavailability was better than the application of single humic acid or lime.