Temporal Effects of Bradyrhizobium Inoculation and Organic Fertilizer Combinations on Microbial Activity in Improving Soil Health

Abstract

Improving soil microbial activity is a critical factor for sustainable agriculture and soil health. This research was conducted to examine the temporal effects of Bradyrhizobium japonicum inoculation and different fertilizer applications on soil microbial activity. The experiment was conducted under pot conditions with eight different application groups (control, urea, vermicompost, Well-rotted farmyard manure and their combinations with bacterial inoculation). Soil respiration (CO₂ release), dehydrogenase activity (DHA) and indole-3-acetic acid (IAA) production capacity were measured weekly during the four-week incubation period. The results showed that organic fertilizer applications increased soil respiration by 46-231% compared to the control. The combination of Bradyrhizobium japonicum and organic fertilizers, especially the combination of Well-rotted farmyard manure (BA+FYM), provided the highest activity values in all parameters. Chemical fertilizer (urea) application showed low activity levels similar to the control group. Soil microbial activity increased rapidly in the first weeks, reached its peak in the third week, and showed a relative decrease in the fourth week. These findings indicate that organic fertilizers and Bradyrhizobium japonicum inoculation strengthen the soil microbial ecosystem and can be used as an alternative to chemical fertilizers in sustainable agricultural practices.