| Aerobic composting technology is one of the most effective ways to treat livestock manure,which can reduce the activity of heavy metals in livestock manure and produce high-quality organic fertilizer.Applying organic fertilizer to plant crops can not only increase crop yield,but also alleviate the barren problem caused by long-term farming.Therefore,it is of great significance and value to optimize the aerobic composting products of livestock manure.However,the problems such as large amount of livestock manure,difficult treatment,secondary pollution,low microbial activity,slow fermentation,low maturity and heavy metal pollution risk of traditional aerobic composting need to be solved urgently.However,the influence of different additives on aerobic composting process and the influence of compost products on crops and soil environment are not clear enough.Aiming at the above problems,this study also provides a scientific reference for optimizing the production and use of aerobic composting of chicken manure,and formulates the following research contents:In this paper,chicken manure was used as the raw material,and the effects of additives on the parameters of aerobic composting of chicken manure and the fertilizer efficiency of the produced organic fertilizer were explored from three aspects.Firstly,the moisture content,carbon-nitrogen ratio(C/N)and inoculum of aerobic composting of chicken manure were optimized by heap temperature,p H,electrical conductivity(EC),seed germination index(GI)and organic matter(OM),and the best initial moisture content,C/N ratio and inoculum of chicken manure composting were selected.Secondly,under the optimal conditions,microbial inoculum,biochar,medical stone and calcium magnesium phosphate fertilizer were used for aerobic composting of chicken manure.The effects of additives on the basic properties,organic matter,humic acid/humus(HA/HS),water-soluble organic carbon(DOC),heavy metal content and morphology of compost and its products were investigated.Meanwhile,the humic acid was characterized by UV-vis spectrum,3D-EEM spectrum and infrared visible spectrum.Finally,the compost products were used to plant pakchoi in pot,and the compost quality was evaluated and analyzed from the basic properties of planting soil,the content and form of heavy metals in pakchoi,and the relationship between the content of heavy metals in pakchoi plants and the total amount of heavy metals in soil was further explored by using data statistical analysis method.The main conclusions are as follows:(1)The experiment of optimizing initial conditions of composting shows that the best initial conditions of aerobic composting of chicken manure are water content of 60%,C/N of 25,and the inoculum is the best microbial agent.The initial moisture content of compost of 60% is more conducive to the start-up of compost fermentation,provides a more suitable environment for microbial activities and oxygen distribution,effectively reduces the conductivity and nitrogen loss of compost,improves the degradation of organic matter,and is more conducive to compost fermentation as a whole.When the initial C/N ratio of compost is25,the GI value of compost products has reached 2.15 on the 45 th day,and the degradation rate of organic matter has reached 15.51%.Under this condition,the microbial activity can be promoted,and the maturity of compost can be improved.The experiment on the influence of inoculum on the properties and maturity of chicken manure compost showed that the high temperature period(> 55℃)of the compost was maintained for 11 days by adding inoculum(mainly composed of Bacillus subtilis and Trichoderma harzianum),and on the 45 th day,the degradation rate of organic matter in the compost reached 16.05%,and the GI value of the compost reached 2.75,which indicated that the inoculum could effectively increase the decomposition and transformation of organic components in the material and the maturity of the compost.To sum up,under the optimal initial moisture content,C/N ratio and inoculum conditions,the safe utilization of organic fertilizer can be effectively guaranteed.(2)Effects of additives on physical and chemical properties,heavy metal forms and humification degree of compost showed that additives improved the maturity and quality of compost,passivated Cu and Zn heavy metals,and affected the molecular weight and aromatization degree of humic acid.The addition of Ca-Mg-P fertilizer reduced the exchangeable distribution rates of Cu and Zn by 1% and-2%,while increased the distribution rates of reducible and residual Zn by 22% and 12%.The UV-vis and 3D-EEM spectra of humic acid showed that the addition of Ca-Mg-P fertilizer increased the content of quinones,components 2 and 3 and the molecular weight of humic acid.On the 45 th day,adding biochar increased the total Kjeldahl nitrogen content of compost by 27.52% compared with the initial compost,and HA/HS increased by 5.36% compared with CK,which indicated that biochar was helpful to improve the humic degree of compost,and had obvious nitrogen fixation.The organic matter degradation rate of compost treated with microbial inoculum reached 29.71%,and the GI value increased by 32.85% compared with CK.Compared with the initial compost,adding microbial inoculum reduced the exchangeable and reducible distribution rates of heavy metal Zn by 8% and 12%,and the exchangeable and reducible distribution rates of heavy metal Cu by 2% and 1%,which indicated that microbial inoculum could effectively reduce the activities of heavy metal Cu and Zn.Adding medical stone reduced the exchangeable state of Cu and Zn in compost by 2% and 6%,and reduced the distribution rate of reducible state by 4% and 12%.The infrared spectrum data showed that adding medical stone could improve the aromatization degree of humic acid in compost,reduce the activity of Cu and Zn in compost and promote the formation of humic acid structure.To sum up,compared with the other three additives,the microbial inoculum has more remarkable effects in promoting the degradation of organic matter and passivation of Cu and Zn,but the p H value,electrical conductivity,seed germination index and water-soluble organic carbon equivalent of the four additives all meet the composting standards.(3)The effects of compost products on crops and soil show that compost products with different additives can increase the yield and quality of Chinese cabbage,and reduce the absorption and accumulation of heavy metals Cu and Zn by Chinese cabbage.Meanwhile,the application of organic fertilizer can increase the organic matter content of soil and enhance the sustainable development ability of soil,and the overall planting benefit of microbial compost products is the best.Firstly,compared with common compost,the application of compost with calcium magnesium phosphate fertilizer increased the yield of Chinese cabbage by 2.5 times,the plant height by 49.9% and the soluble sugar content by 6.29 times.Fertilizer application and compost of calcium magnesium phosphate fertilizer will reduce the p H value of soil.Fertilizer application can significantly increase the nitrate content of Chinese cabbage to2666.13 mg/kg(p<0.05).Fertilizer application can increase the Cu content of Chinese cabbage plants to 20.85 mg/kg,which is 87.67% ～ 190.38% higher than other treatments.Meanwhile,fertilizer application can increase the EDTA-extracted Cu content of soil by6.52%.Compared with CK,the root length of Chinese cabbage was increased by 58.23% and the Cu content of Chinese cabbage was decreased by 8.18%,which was increased by 8.44% ～174.8% compared with other treatments,indicating that the compost treated with microbial agents could reduce the Cu absorption of Chinese cabbage.The content of Zn in pakchoi plants with common organic fertilizer is as high as 53.38 mg/kg,which is the highest among all treatments,and the distribution rate of exchangeable Cu in soil is increased by 9%,which indicates that the application of organic fertilizer without additives can not reduce the accumulation of heavy metal Zn in pakchoi.The vitamin C content of pakchoi treated with blank and adding medical stone was 3.5 times and 3.25 times of that treated with chemical fertilizer,respectively.After applying organic fertilizer,the content of organic matter in soil increased by 68.6% ～ 89.22% compared with the blank and chemical fertilizer treatment,and it was significant with CK(P < 0.05).To sum up,four kinds of additive compost products have their own advantages in the actual cultivation of Chinese cabbage,but from the overall and long-term application risk analysis,it is concluded that microbial inoculum is the best aerobic additive for chicken manure;However,a large amount of organic fertilizer will also increase the risk of Cu and Zn in soil,so it is necessary to apply microbial organic fertilizer scientifically. |
