Microbial structure of nitrogen utilizers in Populus nigra L. compost and vermicompost

Abstract

Abstract Eisenia fetida worms affecting the amount of bacteria from four trophic groups in poplar leaf litter vermicompost was investigated. As a control, composted and vermicomposted horse manure was used. The number of ammonifiers in the vermicomposted manure was higher than in the composted; the opposite situation was observed in poplar litter substrates – the number of ammonifiers was higher in compost than in vermicompost. Nitrogen fixers of the genus Azotobacter were detected only in vermicomposts and were absent in composts. The activity of nitrogen fixers of the genus Azotobacter was higher in vermicomposted poplar leaf litter than in vermicomposted manure. The total amount of ammonifiers and utilizers of inorganic nitrogen is considered to be an integral indicator of the quality of organic fertilizers. This indicator was independent of the presence or absence of worms and was higher in the substrates based on poplar leaf litter compared to the ones based on manure. As the amount of nitrate nitrogen (NO3-nitrogen) is larger in the leaf litter substrates than in the horse manure substrates, we recommend using composted and vermicomposted poplar leaf litter as organic fertilizer with a microbial structure, which provides enough nitrogen available to plants.