Study On Soil Environment Effect Of Sewage Sludge Biochar Land Utilization In Warm-temperate Poplar Plantation

In this study,sewage sludge biochar was imported into the soil of artificial poplar forest in temperate zone,to explored the soil environmental effects of sludge biochar land application.To verify the feasibility of sludge land application disposal way,soil fertility,environmental pollution and ecological risk and microbial and plant characteristics were explored.The amount of sewage sludge biochar used in the field trial was 0 t·hm^-2?15 t·hm^-2?30 t·hm^-2?60 t·hm^-22 respectively,and each amount set up with five repetitions.The basic physical and chemical indexes and nutrient indexes of soil in different seasons after applying different amounts of sludge biochar were investigated.The results showed that sludge biochar could significantly improve soil environment and improve soil fertility.The experimental soil belongs to the typical high pH and low EC soil,which not conducive to the absorption of nutrients.After the application of sewage sludge biochar,pH?H₂O?decreased significantly with the increase of sludge biochar dosage,which decreased from 8.66 much to 8.49;and electrical conductivity?EC?value of soil increased by 3.23-25.64%.Soil organic matter,total nitrogen and total phosphorus increased by 18.36-67.99%,6.96-46.44%and 25.12-89.45%respectively.Sewage sludge biochar can improve the content of trace elements in soil,especially S and B,which were improved by 18.56-57.81%and 16.73-36.75%respectively.The results of soil fertility evaluation before and after application of sludge biochar by improved Nemerow index method,results showed that:soil comprehensive fertility index F increased from 1.18 to 1.40 in summer and from 1.10to 1.31 in autumn,respectively.The F_i values of total phosphorus and available phosphorus in soil were higher,which are the dominant factors,while the organic matter and total nitrogen with lower F_i,are the limiting of factors soil comprehensive fertility.The effect of SSBC on soil microorganisms was explored from the points of enzyme activity and microbial carbon?MBC?and microbial nitrogen?MBN?.The activities of beta-glucosidase?BG?,protease?LAP?and N-acetyl-glucosidase?NAG?increased by 17.85-44.50%,24.99-70.46%and 17.85-44.50%respectively in SSBC treatment group.The correlation analysis showed that BG,LAP and NAG were positively correlated with most parameters.Principal component analysis showed that BG,LAP,NAG,SOM,TN,TP,NO₃^--N,available phosphorus were the dominant factor of soil comprehensive fertility improved by SSBC,while alkaline phosphatase,MBC and NH₄⁺-N were the primary limiting factors.SSBC also introduces pollutants such as heavy metals.After adding biochar,maximum increasement of seven metal elements contents in soil followed Cu>Zn>Ni>Cr>Pb>Hg>Cd,which were 763.66%>141.35%>91.51%>81.12%>80.09%>68.15%>38.19%.However,all of the seven metal elements meet the risk control standards of agricultural land soil pollution.Each metal contamination status and potential contamination risk of soil were assessed by using the geo-accumulation index GI and potential contamination index CP.The evaluation results of heavy metal pollution by Nemerow's synthetic pollution index show that,the risk of single heavy metal pollution and their comprehensive pollution risk increase with the amount of SSBC used,but no pollution is caused.Potential ecological risk assessment results indicated HS group had moderate ecological risk,mainly caused by Hg and Cd.The DBH of poplar was the largest in MS group,which was 6.64-7.24%higher than CK;while relative growth was the largest in LS group,which increased by32.36%on average compared with May.SSBC significantly promoted the nutrient uptake,the biomass of poplar capillary root was 11.60-57.46%higher than CK,content of N was 15.16-48.09%higher than CK,and there was a linear correlation between them.