Effects Of Biochar And Earthworm Cast On Cr-contaminated Soil And Growth Of Potted Rapeseed

In recent years,the problem of soil ecological environment caused by heavy metals has become an important factor restricting the sustainable development of Chinese agriculture.However,the farmland in taiyuan sewage irrigation area is seriously polluted by heavy metals,which endangers human health through the food chain.In order to evaluate the improvement of chromium contaminated soil by biochar and earthworm cast and the feasibility of potted rapeseed,the experiment was divided into two parts:(1)Cr-contaminated soil was treated with three doses(0.3%,0.6%,0.9%)of different biochar(MBC of corn straw biochar,RBC of rice husk biochar,WBC of wheat straw biochar),without biochar as control(CK),effects of different treatments on soil and rapeseed were studied by pot experiment,the basic chemical properties of soil,soil enzyme activity,total amount of Cr in soil,biomass of upper part of potted rapeseed biomass and Cr content were detennined.(2)Cr-contaminated soil was treated with earthwonn cast(4%E,8%E,12%E)and biochar(2.4%B,4.8%B,7.2%B)at different doses,without biochar and earthworm cast as control(CK),effects of different treatments on soil and potted rapeseed were studied by pot experiment.The basic physicochemical properties of soil,the total content of heavy metal Cr,the biomass and Cr content in upper part of potted rapeseed biomass and were detennined.The main research results are as follows:(1)Different WSB/RSB/MSB treatments siunificantly increased the contents of nutrients and the activities of sucrase,urease and phosphatase in soil contaminated with heavy metal chromium(P<0.05).Different WSB/RSB/MSB treatments significantly increased the contents of nutrients and the activities of sucrase,urease and phosphatase in soil contaminated with heavy metal chromium(P<0.05).With the increase of WSB/RSB/MSB,soil nutrient content,sucrase,urease content and rape biomass were significantly increased.Among them,organic matter,available potassium and sucrase changed significantly with the increase of application amount,while total nitrogen,alkali-hydrolyzed nitrogen,total phosphorus and total potassium might not have significant difference between treatments due to small application gradient.(2)Under different WSB/RSB/MSB treatment,soil available phosphorus content,phosphatase and catalase activity all showed the trend of RSB>MSB>WSB.The content of available phosphorus and the activity of phosphatase in soil increased and then decreased with the increase of dosage.Soil catalase activity was significantly increased only at RSB0.3%(P<0.05).At the same dosage,the catalase activity decreased significantly compared with 0.3%when the dosage increased to 0.9%.(3)Under different WSB/RSB/MSB treatment,the fixation effect of chromium in soil was obvious,and the content of chromium in rape was significantly reduced.However,there was no significant difference in chromium content between the biochar and the applied amount.The applied amount of biochar was relatively low,and the difference in applied amount gradient was small,failing to reach the minimum limit of adsorption fixation.Therefore,in the following experiment,the corn straw biochar with the best effect was applied to increase the amount of biochar for further study.(4)The combination of WSB and EWC could regulate the pH of Cr-contaminated soil and improve the nutrient content in soil.As the amount of EWC increases,the pH of soil is getting closer to 7.The contents of total nitrogen,total phosphorus and total potassium were the highest under 8%E+7.2%B treatment.Under 12%E+7.2%B treatment,the contents of available potassium and alkali-hydrolyzed nitrogen were the highest.However,under 12%E+4.8%B treatment,the effective phosphorus content was the highest,and the biochar was significantly reduced to 7.2%.(5)With the increase of the application amount of earthworm cast and biochar,the stronger the inactivation effect of chromium in soil is,the more the biochar and earthworm cast can immobilize and add chromium in soil.WSB and EWC application significantly increased the biomass of the upper part of the planting rape plot in chrome-polluted soil.The biomass of rape increased with the increase of earthworm cast application,but with the increase of carbon application,the biomass of rape showed a trend ofdecrease,but the decrease was not significant.In general,8%～12%E combined with 7.2%B has the best remediation effect on Cr-contaminated soil,can significantly alleviate the toxic heavy metal chromium,improve the possibility of potted rapeseed,and has a positive impact on soil and rapeseed.