Nitrogen-cycling bacteria of the typical soil types in Vojvodina (Serbia): Insights into the relationship with soil chemical properties

Soil quality monitoring is essential in agricultural regions such as the Autonomous Province of Vojvodina, Serbia. The abundance of bacterial functional groups involved in the nitrogen cycle presents a good indicator of nitrogen forms in soil and soil fertility. This study aimed to assess the abundances of selected bacterial functional groups across three different soil types in Vojvodina and to examine their correlation with soil chemical properties. Analyzed soil types (chernozem, solonchak, vertisol) were sampled at nine locations, with two agricultural and one control plot at each location. The abundances of nitrogen-fixing bacteria, ammonifiers, nitrifiers, denitrifiers, and total heterotrophic bacteria were determined. Results showed differences in the abundances of nitrogen-fixing bacteria, ammonifiers, and nitrifiers across different soil types. Chernozem had the highest abundance of nitrogen-fixing bacteria and ammonifiers. Denitrifiers were most abundant in solonchak, while vertisol had the highest abundance of nitrifiers and total heterotrophic bacteria. A statistically significant moderate correlation was observed between the abundance of bacteria and certain soil chemical properties. Namely, moderate negative correlation between nitrifiers and pH in KCl (r=-0.57), pH in H2O (r=-0.53), and CaCO3 content (r=-0.4) and moderate positive correlation between denitrifiers and P2O5 content (r=0.4) were determined. Moderate correlation of bacterial counts and soil properties could indicate that bacterial count variability is also linked to other factors, such as soil vegetation cover type, soil use, anthropogenic activities and climate change. Thus, bacterial functional groups could be useful as an indicator of overall soil health and fertility, especially in connection with nitrogen, as an essential element.