The Effect Of Eisenia Fetida On Nitrogen Metabolism During Corn Straw Composting

China is an important global agricultural country with abundant straw resources.Corn straw is abundant in nitrogen,phosphorus,potassium,calcium,magnesium and organic matter,etc.It is a renewable biological resource.At the same time,the large amount of corn straw can put a burden on environmental protection if not handled properly.In recent years,vermicomposting has become a widely accepted way to degrade corn straw,and the nitrogen metabolic pathways during the composting process have received a lot of attention from researchers.In this paper,Eisenia fetida were inoculated in the process of straw composting to study the effect of E.fetida on nitrogen metabolism in the process.In this study,the composing substrate consisted of corn straw and cow dung,and different experimental groups A（100%corn straw）,B（corn straw:cow dung=60:40）,C（corn straw:cow dung=40:60）and D（100%cow dung）were set up according to the ratio.Each treatment was divided into four groups according to the number of E.fetida inoculated per kg of substrate:0,60,120 and 180 E.fetida respectively.And the all experimental groups were labeled as A₁,A₂,A₃,A₄;B₁,B₂,B₃,B₄;C₁,C₂,C₃,C₄;D₁,D₂,D₃,D₄.The experiment was divided into two phases:pre-composting and formal composting.Every 15 days sampling was conducted to determine the physicochemical properties,enzyme activity changes,gas emission and microbial community structure changes of the substrate.The main study findings are as follows:（1）During the vermicomposting process,the substrate is continuously decomposed and the color of the substrate gradually becomes darker.The inoculation of E.fetida facilitated the stabilization of p H in the substrate,and the p H was stable around 7.0 at the end of the experiment.The electrical conductivity in substrate showed an increasing trend in general,with a range of 476-1027μs cm^-1.The content of total nitrogen and nitrate nitrogen in the substrate showed an increasing trend;the C/N showed a decreasing trend;the ammonium nitrogen and soluble organic nitrogen in the substrate showed an increasing trend followed by a decreasing trend.The compost substrate reached a stable state at the end of the experiment.（2）Ammonia monooxygenase,nitrite reductase and nitrate reductase are key enzymes in ammonia oxidation and play a role in nitrification and denitrification.Ammonia monooxygenase activity showed a trend of increasing and then decreasing,the ammonia monooxygenase activity of group B₃ was 0.0170 U mg^-1 at day 75.Nitrite reductase and nitrate reductase enzymes showed an overall decreasing trend with time,and the nitrite reductase enzymes were 0.327 mg NO₂^—N g^-1 24h^-1 and the nitrate reductase enzymes were 18.140 mg NO₃^—N g^-124h^-1 in group B₄at the end of vermicomposting.The inoculation of E.fetida affected nitrification and denitrification processes,and different variations in enzyme activity were also exhibited in different substrates.（3）The Shannon index was greater in groups B₁₃,B₂₃ and B₄₄ in the sequenced samples,and the community diversity was higher.During vermicomposting Rhodococcus,Mycobacterium and Actinomyces were the dominant genera,and Actinobacteria and Proteobacteria were the dominant phylum.The percentages of community abundance of Escherichia,Mycobacterium,Agromyces and Bosea in the substrate were increased by the inoculation of E.fetida.The inoculation of E.fetida increased community diversity in the composting substrate.（4）N₂O and NH₃ originate from the nitrogen metabolism during vermicomposting.The N₂O emissions are mainly concentrated in the formal composting process.Cumulative N₂O emissions in groups A and B are less than in groups C and D.The N₂O emission fluxes in groups A and B showed an increasing trend with time,while those in groups C and D showed an increasing and then decreasing trend with time.The flux of N₂O emission in group B₄ on day 60was 0.004 mg kg^-1 d^-1.The NH₃ emissions from the composted substrate in group B were mainly concentrated during the pre-composting period,with the peak occurring on day 3.