Effects of preceding crops on potassium dynamics, bacterial communities in tobacco-planted soils, and potassium allocation in tobacco plants

Crop rotation is a key strategy to mitigate the challenges associated with tobacco monoculture, such as soil nutrient depletion and microbial community imbalance. This study investigated the effects of different preceding crops-continuous tobacco (CK), barley (T1), and rapeseed (T2)-on soil potassium (K) forms, K uptake and allocation in tobacco plants, and soil bacterial communities. A randomized complete block design was employed with three replications per treatment. Soil samples were collected at multiple time points to analyze dynamic changes in various K forms (total K, available K, exchangeable K, non-exchangeable K, water-soluble K, mineral K). The bacterial community composition was assessed via 16 S rRNA gene sequencing at tobacco maturity. Key findings include: (1) Preceding crops T1 and T2 significantly enhanced soil available K (increased by 0.55-1.65 times), exchangeable K (1.85-5.77 times), and water-soluble K (3.35-7.23 times) compared to CK at maturity, and promoted the release of non-exchangeable and mineral K. (2) At harvest, the leaf K content in the T2 treatment reached 3.17%, significantly higher than in CK, indicating improved K allocation to leaves. (3) Bacterial community richness (Chao1 index) and diversity (Shannon index) were highest in T2, followed by T1 and lowest in CK. The dominant phyla were Proteobacteria, Actinobacteria, and Acidobacteria, whose relative abundances increased under rotation. The rapeseed rotation (T2) most effectively enhanced soil K supply, bacterial diversity, and leaf K accumulation. These results demonstrate that selecting appropriate preceding crops, particularly rapeseed, can optimize soil K availability, improve bacterial community structure, and enhance potassium utilization efficiency in tobacco, providing a theoretical basis for sustainable tobacco cultivation.