Research And Development Of Three Bioremediation Agents For Herbicides Contaminated Soil

China is a large country of agricultural production,and herbicides are widely used in agricultural production.The sulfonylurea herbicide bensulfuron-methyl,the diphenyl ether herbicide lactofen,and the triazene herbicide metribuzin have been widely used in weed control in the field because of their low toxicity and high efficiency.With the decrease of the rural labor force and the improvement of weed resistance level,the residue of herbicides in the soil is becoming increasingly prominent,which brings potential risks to the ecological environment.Microbial remediation of herbicide residues is a safe,efficient,and no secondary pollution method.At present,the research on the remediation of herbicide-contaminated soil mainly focuses on the isolation and screening of degrading microorganisms and the elucidation of the degradation mechanism.There are few pieces of research on the development of microbial herbicide-degrading agents and optimization of their preservation conditions.However,the problem of the short shelf life of microbial agents has restricted the large-scale production and application of degrading microbial agents.Therefore,in this paper,the highly efficient degradation strains Hansschlegelia zhihuaiae S113,Bacillus sp.Za and Rhodococcus sp.QCT-10 was served as material to study the best ratio of liquid bacterial protectants,different preservation formulations of solid bacterial agents,and the preliminary application of solid bacterial agents,which provided a theoretical basis for the preservation and application of three herbicide degrading bacterial agents.The main contents and results of this study are as follows.Firstly,the effective preservation of three herbicide degrading bacteria liquid inoculants was studied.By adding protective agents to the inoculants,the effective number of living bacteria and degradation rate were improved.The results showed that,compared with the control,adding 0.30%sodium citrate,0.20%carboxymethyl cellulose,and 0.10%Ca Cl2 to S113 liquid bacterial preparation could increase the viable count by 37.25%,and the effective viable count was 1.53×10~6 cfu/m L after 120 days storage.Adding 0.20%sodium citrate,0.20%carboxymethyl cellulose,and 0.30%KCl to Za liquid bacterial preparation could increase the viable count by 35.71%,and the effective viable count was1.02×10~8 cfu/m L after 120 days storage.Adding 0.10%sodium acetate,0.30%carboxymethyl cellulose and 0.30%KCl to QCT-10 liquid bacterial preparation could increase the viable count by 39.08%,and the effective viable count was 2.42×10~7 cfu/m L after 120 days storage.The results of the herbicide degradation test showed that after 30days of storage,S113 liquid bacteria could degrade 94.25%of bensulfuron methyl with a concentration of 50 mg/L within 3 days,Za liquid bacteria could degrade 83.50%of lactofen with a concentration of 50 mg/L within 3 days,and QCT-10 liquid bacteria could degrade 80.97%of metribuzin with a concentration of 50 mg/L within 3 days.Then,choose peat,chicken manure,earthworm manure,straw manure,pig manure,peanut shell powder,rice bran,and sanmei organic fertilizer as adsorption carriers to develop solid microbial agents.The results showed that the water content of the selected carrier was between 6.30%-16.21%,the p H value was between 6.0-8.0,and the water absorption rate was more than 30%,which met the carrier standard for solid bacterial agents.The carrier is prepared as a solid bacterial agent,the results showed the highest number of viable bacteria was 6.73×10~6 cfu/g in S113 with organic fertilizer as the carrier,5.56×10~7 cfu/g in Za with pig manure as the carrier,and 5.31×10~7 cfu/g in QCT-10 with sanmei organic fertilizer as the carrier.A pot experiment was used to study the degradation effect of the solid microbial agent after 120 days of storage.The results showed that the S113 solid bacterial agent with sanmei organic fertilizer as the carrier could degrade bensulfuron methyl in 10 mg/kg dry soil by 91.22%in 7 days,the Za solid bacterial agent with earthworm manure as carrier could degrade lactofen in 5 mg/kg dry soil by 85.52%in7 days,the QCT-10 solid inoculum with sanmei organic fertilizer as the carrier can degrade79.46%of metribuzin at 5 mg/kg dry soil within 7 days.Finally,the preliminary application of solid bacteria was studied.The results showed that the optimum inoculation amount of S113 and QCT-10 was 10%,and the optimum inoculation amount of Za was 7%.The degradation effect of the three kinds of solid bacteria was the best when they were added to the soil by mixed fertilization.Pot experiment of plants showed that the herbicide residue in soil could be effectively degraded and the damage of herbicide residue to corn and soybean could be repaired by adding solid bacteria agent of herbicide degrading bacteria.The physiological indexes of maize plants treated with S113 and Za returned to the level of the control group after 21 days,and the effect of QCT-10 on soybean plants was not obvious after 14 days.At 21 days,the average stem and leaf length of the corn group treated with S113 and Za were 13%higher than that of the control group,and the stem and leaf length of the soybean group treated with QCT-10 was 17%higher than that of the control group.