Study On Vermicomposting Of Garden Waste And Its Comparision With Cow Dung

With the rapid development of urban greening in China,the disposal of garden waste has become an urgent problem to be solved.Vermicomposting is a rapid and efficient method that utilizes earthworms and microorganisms to decompose organic waste and convert it into high-quality fertilizer.Compared with other treatment methods of organic waste,vermicomposting is simple,affordable,and has high fertilizer production efficiency.However,the past studies on garden waste are mainly about composting and use it as an additive to other substances for vermicomposting.The utilization of garden waste alone as a substrate for vermicomposting needs to be further analyzed.Cow dung is considered to be an excellent substance and has been widely studied.We performed vermicomposting with garden waste as the only substrate and compared it to vermicomposting with cow dung.The changes of the physical and chemical properties in the garden waste and cow dung,as well as the biological parameters of the earthworms during 60 days vermicomposting were investigated.Then,the changes of physical structure properties and microbial community structure in different substrates before and after vermicomposting were studied.Finally,it is clear that vermicomposting of garden waste as a single material is feasible,and the mechanism of vermicomposting in garden waste and its similarities and differences with cow dung are clarified.It is expected that the results will provide a theoretical basis and technical support for the vermicomposting of garden waste and the agricultural utilization of its vermicompost.The main results are as follows:(1)Vermicomposting process could improve the pH and EC of the garden waste,accelerated the mineralization of the organic matter,and converted the insoluble particles into a soluble form.After 60 days of vermicomposting,the pH and EC of the garden waste were 8.48 and 2.00 mS·cm-1,respectively.At the meantime,the vermicomposting process could increase percentage content of total nitrogen,total phosphorus,total potassium,available phosphorus and available potassium in garden waste,but the above indicators in garden waste were all lower than cow dung.Besides,the burrowing behavior of earthworms could affect the aerobic conditions in the substrate and promoted nitrification.Inorganic nitrogen was significantly increased after 60 days vermicomposting in different treatments.The above results show that vermicomposting could change the physical and chemical properties of garden waste and improve its nutritional values.The nutritional value of the vermicompost depends on the characteristics of the raw materials.Although in terms of total nutrients and effective nutrients the vermicompost of garden waste was lower than cow dung,it also has high land use value.(2)In garden waste,no death or escape of earthworm occurred,and the average body weight of earthworm remained at around 0.4 g for the first 40 days and reduced to 0.277 g in the 60 day.In cow dung,the survival rate of earthworm showed a tendency of slow decline and finally maintained at about 56.7%.The average body weight showed a pattern of rising first and then decreasing.The number of cocoons in the two substrates also showed a trend of increase initially followed by a decline with time.At the 30 day,the number of cocoons reached the maximum value and we found approximately 200 cocoons in garden waste,which was significantly less than the 265 cocoons found in cow dung.The biological parameters of earthworms indicate that garden wastes are also suitable for the growth and reproduction of earthworms.It is feasible to vermicomposting using garden waste.The main factors affecting the growth and reproduction of earthworm in physical and chemical properties are organic matter,C/N ratio and EC.Therefore,the nutrient content of the substrate and the control of the appropriate range of C/N ratio,EC and pH in the substance is of great significance for an efficient vermicomposting process.(3)Scanning electron microscopy images showed that the initial materials contain large granular units and rod-like structures,and these structures in its vermicompost were severely destroyed and degraded into fluffy and granular debris.Similar with cow dung,vermicomposting of garden waste could effectively degrade the compact physical structure into fragmented porous particles,increasing its agricultural application value.Specific surface area analysis showed that the adsorption-desorption isotherms of all samples belonged to type III,indicating that garden waste and cow dung was a slit-like pore composed of loose polymer flaky particles.Although the surface area,pore volume,and pore size of garden waste were smaller than that of cow dung,the vermicomposting process could also increase its surface area and porosity,and improve the water holding capacity of the vermicompost.It can be seen from the thermogravimetric analysis that due to the increase of aromatic compounds in garden waste,there were more heat-resistant components than cow dung.In addition,the residual mass fraction of the vermicompost after thermal degradation was slightly higher than that of the raw material,and the peak intensity of the mass loss rate decreases,indicating that the easily degradable compound in the raw materials was converted into a more complex compound in the vermicompost and vermicompost has a higher stability than the raw material.(4)Vermicomposting could increase the richness and diversity of the bacterial community.Garden waste had a higher bacterial community richness after vermicomposting,and cow dung had a higher bacterial community diversity.The dominant groups of bacterial communities at the phylum level were Proteobacteria,Bacteroidetes,and Actinobacteria.Among them,Proteobacteria was the phylum with the highest relative abundance,and its proportion in garden waste was much higher than that of cow dung.After vermicomposting,a significant reduction in Proteobacteria was observed in vermicompost,with an increase in the relative abundance of the Planctomycetes and Acidobacteria.At the genus level,the composition of the two substrates and before or after their vermicomposting were quite different.The dominant groups were mainly Allorhizobium,Pseudomonas,Novosphingobium,Flavobacterium and Streptomyces.Cluster analysis showed that the source of materials was the main influencing factor affecting the similarity of the bacterial community and the vermicompost of different substrates were similar in bacterial community structure.In addition,the physical and chemical properties of substrates significantly affected the dynamic changes of bacterial community structure.