Isolation of nitrogen-fixing bacteria from vermicompost applied soil and determination of their potential as microbial fertilizer

With the increase in the use of chemical fertilizers, pesticides and similar substances in agriculture the fertility of the soils decreases day by day, and negative situations occur in terms of environment and human health. Therefore, it is thought that the demand for materials and biological preparations without side effects such as organic fertilizers and microbial fertilizers should increase. In this context, this study aims to isolate nitrogen-fixing bacteria from vermicompost applied soil and to determine microbial fertilizer potentials. In the scope of the study, nitrogen-fixing bacteria were isolated from the rhizosphere area of the plant growing in soil treated with vermicompost. Results of 16S rDNA sequence analysis, 5 different isolates (N1DBA-5, NHBA-1, NHBD-5, NNBD-7 and N1DBD-4) were selected for potting trials according to their growth conditions in different media and colour and shape differences. The potting experiment was carried out with two different control groups, according to the randomized plot design, with a total of 35 pots with 5 replications. Curly lettuce (Lactuca sativa var. Crispa) was used as the test plant in the experiment. Biological analyses (urease activity, alkaline phosphatase activity, β-glycosidase activity, dehydrogenase activity and mesophilic bacteria count) and chemical analyses (mineral nitrogen forms, macro-micro nutrients and pH-EC measurements) in soil samples taken at the end of the trial (normal-rhizosphere) have been done. Besides, the yield and quality parameters of the harvested plant samples were measured and macro and micro nutrient analyses were performed. According to the results, it has been observed that some isolates have positive effects some of the parameters analyzed. In this context, it was determined that isolates N1DBD-4, NHBA-1, NNBD-7 and N1DBA-5 were effective in the soil and only the isolate N1DBD-4 resulted in some changes in the plant. However, it is thought that N1DBD-4 isolate can adapt to the rhizosphere conditions better than other isolates. It is assumed that the mentioned isolate may have microbial fertilizer potential as it is partially more beneficial than others in terms of both soil fertility and plant efficiency.