Effect Of Three Spent Mushroom Substrate Amendments On Cadmium Polluted Greenhouse Soil Remediation And Rape Growth

As greenhouse agriculture expands rapidly,greenhouse soil heavy metal pollution because of the excessive fertilizer application as well as special environment"high cropping index,high fertilizer rate,high temperature,high humidity and no precipitation eluviation"has been a huge problem which can cause risk to food safety and human health.In-situ remediation,which using organic matter as remediation agent is one of the effective methods for planting and remediation of moderately heavy metal contaminated soil.In this study,three kinds of amendments:spent mushroom substrate（SMS）,spent mushroom substrate biochar（SMSB）and spent mushroom substrate compost（SMSC）were prepared from edible fungus cultivation waste-fresh bacterial chaff as raw material,soil culture simulation remediation experiment and greenhouse pot experiment were conducted to study the effects of amendments on soil Cd fractions and rape growth.The main research results are as follows:（1）The greenhouse conditions had effect on the soil available cadmium concentrations.NH₄NO₃,Ca（NO₃）₂,Mg SO₄,Na Cl can cause Cd activation and available Cd concentration rise and NH₄NO₃ had the most significant influence（p<0.05）.As the soil p H decreased from6.4 to 5.94,available Cd concentration increased from 0.95 to 1.43 mg·kg^-1.As incubation temperature rised to more than 30℃and dry-wet circle both promoted available Cd concentration increased,while temperature flooded up to 30℃below,freeze-thaw cycle reduced the available Cd concentration.All three amendments reduced the adverse effects of the greenhouse conditions and decreased available Cd concentration to the level without salt stress.Among three amendments,SMSB had the most obvious effect on offsetting the adverse effect of the greenhouse environment,there is no significant difference between SMS and SMSC’s effect（p<0.05）.（2）Effects of three kinds of amendments on soil Cd immobilization and soil physical and chemical properties were shown in soil culture simulation remediation experiment.The application of three amendments reduced the exchangeable Cd content significantly（p<0.05）,and the degree of decrease increased with the addition of amendment.When the application amount was 4%,the immobilization effect was the best.At the end of culture,4%SMS,SMSB and SMSC reduced the exchangeable Cd content by 29.06%-52.77%,42.94%-59.26%,29.06%-36.47%.Three amendments mainly promoted the conversion of Cd from exchangeable fraction to organic binding fraction,and the above treatment increased the organic binding fraction content by 37.47-59.73%,12.67%to 31.66%,14.74%-29.56%,respectively.The amendments significantly increased the soil p H,the cation exchange capacity（CEC）,the increase of p H were 0.18-0.68,0.47-1.04,0.19-0.44,and increase of CEC were 2.04%-29.72%,3.32%-43.29%,1.49%-31.05%,respectively.In addition,three amendments increased soil water holding capacity,alkali solution nitrogen,available phosphorus and available potassium significantly（p<0.05）.According to the results of the correlation analysis of Cd exchangeable content and soil physi-chemical properties,Cd exchangeable content and p H,cation exchange capacity,water holding capacity,alkali solution nitrogen,available phosphorus and available potassium were significantly negative correlated,Cd exchangeable content and bulk density were significantly positively correlated,Cd exchangeable content and residue,organic combination fraction were significantly negative correlated,Cd exchangeable content and electrical conductivity were not related.In addition to improving soil properties,three amendments also increased soil enzymes activity,Cd inhibited soil enzymes activity,and amendments significantly improved soil enzymes activity（p<0.05）,the improvement degree of SMS on the three enzymes activity was43.33-106.6%,which was close to that of SMSC（48.05%-136.67%）,better than that of SMSB（23.80%-86.87%）.（3）In greenhouse pot experiment,the biomass of rape was increased by three amendments.In vegetable garden soil,the biomass of rape in the SMS,SMSB,SMSC treatment group increased by 6.55%,21.43%,and 54.17%,respectively compared with CK treatment.In greenhouse soil,the growth of rape in each group was inhibited.Compared with the maximum biomass,the biomass of CK treatment,SMS treatment,SMSB treatment and SMSC treatment decreased by 82.88%,62.89%,29.73%and 23.17%,respectively.In vegetable garden soil and greenhouse soil,SMSC treatment group has better promoting effect on rape growth.Three amendments also decreased the Cd content of rape significantly（p<0.05）,decrease were 43.48%,60.87%and 17.39%,respectively.The Cd contents of rape under three treatments were in accordance with edible standard,increase of rape leaf chlorophyll were 2.87%-9.85%,11.75%-16.12%and 14.75%-27.01%,increase of soluble protein were 3.07%-10.42%,13.59%-50.36%and 12.88%-35.75%,increase of soluble sugar were 9.23-9.46%,16.92%-18.92%and 12.31%-13.51%,increase of proline were3.23%-5.92%,7.09%-12.67%and 4.94%-10.56%,increase of POD were 54.66%-74.26%,39.05%-51.13%and 22.19%-49.58%,respectively.These results reflect that the three amendments can effectively promote the growth of rape and alleviate the toxicity of Cd.The three amendments also significantly increased the microbial carbon and nitrogen content of vegetable garden soil and greenhouse soil（p<0.05）:the improvement of microbial carbon and nitrogen by SMS were 8.06%-14.94%and 4.46%-22.86%,the improvement by SMSB were17.49-29.74%and 8.48-25.88%,the increase by SMSC were 12.12%-22.35%and11.05%-31.41%.