Drip Irrigation and Fertilization Strategies Shape Soil Bacterial Community and Nutrient Utilization in Summer Peanut

Optimizing fertilization strategies is key to increasing peanut yields and maintaining soil health, but it is still unclear how the proportion of basal fertilizer (applied before sowing) and topdressing (applied through drip irrigation during growth) systematically affects the “soil microbe plant” system under integrated drip irrigation and water–fertilizer management. This study set up four fertilization strategies—no fertilizer (F1), full basal fertilizer (F2: N–P2O5–K2O = 343.9–123.0–120.0 kg·hm−2 applied at sowing), drip irrigation with full water-soluble fertilizer (F3: total NPK input same as F2, applied via drip irrigation at flowering–pegging, pod-setting, and pod-filling stages in a 6:2:2 ratio), and 50% basal fertilizer + 50% water-soluble fertilizer (F4: basal applied at sowing, water-soluble applied via drip irrigation at the three growth stages in a 2:4:4 ratio)—to explore their effects on the soil nutrient availability, enzyme activity, bacterial community, and plant nutrient uptake throughout the entire growth stage of peanuts. The results showed that drip irrigation and topdressing strategies significantly improved soil-available nutrients and enzyme activity in the later stages of growth, with the F4 treatment showing the most significant advantage. This treatment not only significantly improved bacterial diversity and community functional redundancy and maintained a stable presence of multifunctional beneficial bacterial genera but also significantly increased nitrogen, phosphorus, and potassium uptake and fertilizer use efficiency. Partial least-squares structural equation modeling (PLS-SEM) reveals that fertilization strategies mainly indirectly drive yield increase by regulating microbial communities and enzyme activity. In summary, under the condition of equal nutrient input, the strategy of evenly matching nutrient supply with peanut demand was achieved, which not only ensured high yield and efficiency but also enhanced soil microecological stability. It is the optimal strategy for integrating water and fertilizer into the drip irrigation of summer peanuts under the conditions of this experiment.