Effect of continuous and rotational crop cultivation on nitrification activity and microbial communities in tobacco field soils

Different cropping systems can enhance agricultural sustainability by improving soil physicochemical properties and microbial functionality. This study evaluated the effects of crop rotation on soil microbial community composition, heavy metal accumulation, and nitrification activity in long-term tobacco fields. Soil samples were analyzed for physicochemical properties, nitrification rates, heavy metal concentrations, and bacterial community composition using high-throughput 16S rRNA gene amplicon sequencing. Compared to tobacco monoculture, tobacco jute rotation increased total carbon and total nitrogen contents by approximately 13.5% and 11.2% respectively. Net nitrification rates were significantly higher in tobacco jute rotation (5.4 mg kg⁻¹ h⁻¹), representing nearly a 3.9-fold increase over monoculture systems (1.37 mg kg⁻¹ h⁻¹). Tobacco rice rotation reduced copper (Cu) and zinc (Zn) concentrations by 70.7% and 80.1%, respectively, compared to tobacco maize systems. Microbial community analysis revealed that Pseudomonadota (formerly Proteobacteria) remained the dominant phylum across all systems, with relative abundance ranging from 14.96% to 34.52%. Shannon diversity indices were higher in rotational systems, with tobacco jute showing a 48.5% increase in diversity compared to tobacco maize rotation. These findings demonstrate that crop rotation can improve soil fertility, reduce trace metal accumulation, and restructure soil bacterial communities, thereby offering a practical and sustainable strategy for long-term soil health management in tobacco-based agricultural systems.