Co-application of organic fertilizer and composite microbial inoculant improves soil quality and cotton yield in saline-alkaline cotton fields of southern Xinjiang

Soil salinization and insufficient nutrient supply jointly constrain sustainable cotton production in southern Xinjiang. To clarify how coordinated regulation by organic fertilizer, composite microbial inoculant, and irrigation reshapes the soil-crop system in saline-alkaline cotton fields, a three-factor field experiment with 16 treatments was conducted using organic fertilizer at 0 and 30 t/ha, composite microbial inoculant at 0, 30, 60, and 90 kg/ha, and irrigation at 80% and 100% of crop evapotranspiration (ET c ). The combined treatments significantly reduced soil electrical conductivity, increased soil organic carbon and total nutrient reserves, enhanced extracellular enzyme activities involved in carbon, nitrogen, and phosphorus cycling, and increased the soil quality index. Organic fertilizer was the dominant factor driving bacterial community differentiation, whereas its co-application with a medium rate of composite microbial inoculant favored the enrichment of genera associated with improved soil biochemical conditions. Leucine aminopeptidase, cellobiohydrolase, organic carbon, and N-acetyl-β- D -glucosaminidase were identified as the main soil factors associated with seed cotton yield. The combined treatments also alleviated leaf oxidative damage, improved photosynthetic pigment status, promoted dry matter accumulation, and ultimately increased seed cotton yield. Among all treatments, the combination of 30 t/ha organic fertilizer, 60 kg/ha composite microbial inoculant, and 100% ET c irrigation (F1B2W2) showed the best overall performance, with a seed cotton yield of 6.54 t/ha. These findings indicate that coordinated improvement in salinity status, nutrient reserves, enzyme-mediated nutrient turnover, and bacterial habitat provides a key basis for enhancing cotton productivity in saline-alkaline cotton fields in southern Xinjiang and offers field-based support for optimizing integrated management with organic fertilizer, composite microbial inoculant, and irrigation.