Effects of the potassium-solubilizing bacteria Arthrobacter sp. Y43 and Bacillus sp. H42 on tobacco seedling growth and rhizosphere potassium availability under different inoculation strategies.

Excessive use of chemical fertilizers may contribute to soil degradation and environmental pollution. Potassium-solubilizing bacteria (KSB) have the potential to improve soil K availability and support plant growth. This study evaluated the effects of two KSB strains (Arthrobacter sp. Y43 and Bacillus sp. H42) on tobacco seedling growth and soil available K in separate experiments involving four inoculation timings (small cross, large cross, rooting, and mature seedling stages) and three inoculation frequencies (one, two, or three applications). Plant biomass, culturable microbial counts in the rhizosphere soil, soil enzyme activities, soil K fractions, and leaf K concentration were determined. The results showed that inoculation with Y43 or H42 improved tobacco seedling growth to varying degrees, with the rooting stage considered the optimal inoculation timing for both strains among the timings tested. At this stage, inoculation with either strain significantly increased the counts of culturable bacteria and actinomycetes and decreased culturable fungal counts in the rhizosphere soil. Higher soil enzyme activities, soil available K content, and leaf K concentration were also observed following inoculation. Organic acids and amino acids detected in the culture filtrates of both Y43 and H42 may be linked to soluble K release, and the capsular polysaccharides of H42 may also be involved. Among the frequencies tested, better overall responses were observed after three applications of Y43 and two of H42. This study provides candidate K-solubilizing strains and preliminary information on their application, supporting their further evaluation in tobacco cultivation.