Investigation of the effects of asembiotic bacterial diazotrophs in soil and its interactions with indigenous microbiological properties

In order to maintain soil fertility, there is a need for strategies to improve soil quality and soil health. One of these is to increase the beneficial microbial population in the rhizosphere zone of the soil through biological fertilization (biofertilization). This study was conducted with the purpose of investigating the effectiveness of potential and the effects on current biological properties in soil with Typical xerofluvent properties under Mediterranean climatic conditions of an imported commercial preparation of organisms (Azospirillum sp., Azorhizobium sp. and Azoarcus sp.) which have the ability to bind free nitrogen from the air (N2) by carrying out asymbiotic nitrogen fixation. The experiment was conducted in 2015 on the experimental field of Alaşehir Vocational School, Manisa Celal Bayar University, with a random block design and three replications. Three different doses of chemical nitrogen fertilizer (0-125-250 kg N ha-1; N0-N1-N2) were applied to plots with and without biological fertilizer (0-0.5 g ha-1; BG0-BG1), and the effects of these treatments on soil microbiological activity (microbial biomass carbon – MBC, basal soil respiration – BSR, N-mineralization – Nmin, number of general bacteria – GB, number of Azospirillum sp. – AZO) and biochemical activity (dehydrogenase enzyme activity – DHG, protease enzyme activity – PRO, urease enzyme activity – UA), various soil characteristics, and the yield and nitrogen content of the test plant (Zea mays var. indentata) were investigated on a factorial basis. Biofertilization had a significant positive effect on the microbiological and biochemical parameters MBC, DHG and AZO (P<0.05) examined in the soil; increases were seen in the parameters BSR, Nmin and GB, but these were found not to be statistically significant (P>0.05). Also, although a reduction was seen in the activity of two enzymes of the hydrolase group which take part in the nitrogen cycle in the soil, this reduction was found not to be statistically significant (P>0.05). No clear effect was observed of the applications on the chemical properties of the soil. However, the negative correlation found between NO3-N and AZO (-0.468**) shows that the use of fertilizers containing Azospirillum sp. and NH4-N would be more suitable. In the maize plants, yield showed an increase of 24-69% with the application of biofertilizer, and nitrogen content increased by 3-11%. The application affecting these parameters the most was the N1BG1 application. Evaluating the results of the experiment, it was seen that the biological characteristics of soils and the yield of maize plants are affected positively by a single dose of biofertilizer containing diazotrophic microorganisms applied to soils under Mediterranean climatic conditions. Therefore, it is recommended that biological fertilizer at a dose of 0.5 g ha-1 together with nitrogen at a dose of 125 kg N ha-1 should be used on Typic xerofluvent soils in order to both maintain soil health and support crop yield.