Soil Bacterial Community Responses to Prolonged Organic and Inorganic Fertilization in Dryland Agricultural Systems

A field experiment was conducted to explore how long-term integrated organic or inorganic fertilization influences soil bacterial communities in dryland farming systems. High-throughput amplicon sequencing was applied to profile bacterial composition and diversity under six treatments—no fertilizer (T0), chemical fertilizer alone (T1), and chemical fertilizer combined with cattle manure (T2), sheep manure (T3), bio-organic fertilizer (T4), or potassium fulvate (T5)—and to pinpoint the major environmental determinants. The results showed that combined fertilization markedly elevated soil nutrient levels, with cattle manure (T2) and sheep manure (T3) exhibiting the strongest effects. The bacterial community was dominated by Actinomycetota, Pseudomonadota, and Chloroflexota. Relative abundances of Pseudomonadota and Bacteroidota increased under combined fertilization, whereas Actinomycetota declined—particularly in T2 and T3. At the genus level, Nocardioides, KD4-96, and Subgroup 6 were predominant. Moreover, T2 and T3 significantly raised the Simpson index relative to T1. Redundancy analysis revealed that soil organic matter (p = 0.002) and pH (p = 0.03) were strongly associated with variation in bacterial community composition. Collectively, long-term combined organic-inorganic fertilization with different organic amendments effectively enhances soil fertility and bacterial community structure, offering a promising approach for nutrient management in the dryland farming regions of the Ningxia Hui Autonomous Region, northwestern China.