Bacillus Inoculation and Mineral Nitrogen Fertilization Influence Soil Biology and Plant Growth in Peanut (Arachis hypogaea L.)

The combined use of biofertilizers and mineral fertilizers is of great importance for improving both productivity and sustainability in crop production. In this study, the effects of Bacillus inoculation and nitrogen fertilizer applications, applied individually or in combination, on peanut growth and soil biological properties were investigated. A pot experiment was conducted under greenhouse conditions in 2025. The treatments consisted of four applications arranged with three replications: control, Bacillus (BS), mineral nitrogen (Min-N), and Bacillus + mineral nitrogen (BS+Min-N). Plant height, SPAD value, fresh and dry biomass, leaf temperature, soil enzyme activities (dehydrogenase, protease, catalase, arginine deaminase, and invertase), and soil NH4+ and NO3- concentrations were determined. According to the results, the highest SPAD values and fresh and dry biomass were obtained from the Min-N and BS+Min-N treatments. Leaf temperature decreased under mineral nitrogen applications. Bacillus treatment increased soil protease activity, whereas the BS+Min-N treatment resulted in the highest arginine deaminase and invertase activities. In contrast, dehydrogenase activity decreased in treatments containing mineral nitrogen. Soil NH4+ and NO3- concentrations were significantly higher in the BS+Min-N treatment compared with the other treatments. In conclusion, mineral nitrogen application directly promoted plant growth, whereas Bacillus inoculation positively affected soil biological activity. The combined use of Bacillus and mineral nitrogen produced more favorable outcomes in terms of both plant growth and soil biology. Therefore, the integrated use of Bacillus-based biofertilizers with mineral nitrogen may be recommended to reduce chemical fertilizer use and support sustainable peanut production.