Effects Of Biochar On Immobilization Remediation Of Soil Contaminated By Cadmium And Its Soil Environmental Impact

With the rapid economic development,the problem of heavy metal pollution in farmland soil has become increasingly serious.In 2014,the"National Soil Pollution Survey Report" showed that the rate of over-standard for farmland soil was 19.4%.The problem of heavy metal pollution has caused threats to China's food security and food safety,and farmland soil remediation is imperative.Farmland soil passivation and restoration technology is currently the most widely used and most effective repair method.However,the commonly used passivation materials such as lime will cause soil compaction and crop yield decline after long-term application.Therefore,it is very necessary to explore new passivation materials that can be recycled.Recent studies have shown that biochar can be used as a passivation material for the remediation of heavy metal-contaminated soils,and can effectively reduce the bioavailability of heavy metals in soil.It has considerable potential for restoration,but different biochar materials,different application rates,and heavy metal pollution levels in different soils.The effect of passivation repair may vary greatly.Therefore,in this study,peanut shell biochar was used as a test material to study the effects of different biochar application rates on the growth and Cd uptake of pakchoi cabbage,Cd morphology,soil nutrient content,and enzyme activity under three different levels of cadmium.Influence of microbial diversity,etc.,to explore the effect of biochar on the passivation and remediation of Cd-contaminated soil and the effect of soil environmental quality.The main results are as follows:(1)The addition of biochar can significantly reduce the content of available Cd in the soil.Under the Cd levels of 2.5 mg/kg and 5.0 mg/kg,the ratio of available Cd to total Cd in the soil decreased significantly with the increase of biochar addition,and the L(4)treatment with the largest addition of biochar was H(4)treatment has the largest decline.(2)The addition of biochar can reduce the cadmium uptake of Brassica chinensis.Under the 2.5 mg/kg and 5.0 mg/kg Cd levels,the shoot enrichment coefficient of Chinese cabbage showed a significant downward trend with the increase of biochar addition.Compared with non-addition of cadmium,the cadmium enrichment coefficient of Chinese cabbage treated with L(4)decreased by 75.97%,and the cadmium enrichment coefficient of Chinese cabbage treated with H(4)decreased by 55.94%.(3)The addition of biochar can promote the growth of pakchoi.The biomass of Chinese cabbage planted under three soil Cd levels increased with the increase of biochar addition.When the amount of biochar added was 4%,the biomass without Cd treatment was 1.15 times that of the 5.0 mg/kg Cd treatment,indicating that higher soil Cd content would inhibit the growth of Chinese cabbage.(4)Since the biochar is alkaline,it can significantly increase the pH of the soil after it is applied to the soil.The correlation analysis showed that there was a significant negative correlation between soil pH and the ratio of available Cd in soil to total Cd,indicating that biochar addition can reduce the effectiveness of Cd by increasing soil pH.(5)The contents of ammonium nitrogen,nitrate nitrogen,available phosphorus and soluble organic carbon of the soils treated with different tests showed a decreasing trend with time.Compared with the 28th day,the content of soil soluble organic carbon decreased by 63.42%,64.54%and 49.86%at the 90th day,and the available phosphorus content decreased by 48.99%,61.1%and 59.85%,respectively;With the increase of added amount,the soil available nutrient content showed an increasing trend under the three kinds of Cd levels,of which the O(4)treatment with the largest addition of biochar,the L(4)treatment and the H(4)treatment had the largest increase.(6)Biochar application has a significant effect on soil enzyme activity.Under the three Cd levels,soil urease activity,catalase activity,and alkaline phosphatase activity were higher than those with lower biochar content when biochar was added.However,when the amount of biochar added reached 4%,the activity of the three enzymes in the soil was inhibited,and the activity was lower than that of the soil without added biochar.(7)Biochar addition had a significant effect on soil bacterial diversity,but soil Cd content had no significant effect on soil bacterial community structure.The soil bacterial abundance increased with the increase of biochar addition,but when the biochar addition exceeded a certain limit,the bacterial abundance decreased significantly.