Poly-γ-glutamic acid improves soil structure to enhance seed cotton yield and fiber quality in arid saline regions

Soil salinization has become a prominent global environmental challenge, posing a serious threat toward the irrigated farming systems. Poly-γ-glutamic Acid (γ-PGA) functions as a bio-degradable and eco-benign soil amendment, which is essential for advancing sustainable agricultural development in Xinjiang’s saline-alkali environments. The field experiment (2024–2025) encompassed five amounts: P0 (0 kg·ha −1 ), P1 (7.5 kg·ha −1 ), P2 (15 g·ha −1 ), P3 (22.5 kg·ha −1 ), and P4 (30 kg·ha −1 ). Our results demonstrated that applying γ-PGA markedly elevated the percentage of soil macro-aggregate fractions. Higher γ-PGA levels contributed to augmented soil water storage (SWS) and reduced soil moisture consumption. Concurrently, the soil active accumulated temperature (SAT) of P4 was 34.60% higher than that of P0 in 2024 and 22.79% higher in 2025. Furthermore, increasing γ-PGA accelerated soil desalination rates, strengthened photosynthetic capability, and boosted root growth and biomass accumulation. In γ-PGA application treatments, plant biomass (PB), seed cotton yield (SY), ginning outturn (GO) and fiber quality index (FQI) were improved by 6.52–19.61%, 11.73–30.60%, 3.51–7.62% and 0.28–0.85, respectively. Moreover, γ-PGA improved soil aggregates, SWS, desalination rates, and SAT, which underlay the correlative link between soil attributes and cotton production, and therefore an increase of the SY and fiber quality. The TOPSIS method identified that the ideal γ-PGA dosage was 22.08 kg·ha −1 within arid saline region. The findings emphasized the feasibility of further improving soil environment, SY, and FQI through optimized γ-PGA application rates to facilitate agricultural revitalization in arid saline fields. • Poly-γ-glutamic acid (γ-PGA) was capable of boosting soil aggregate stability. • γ-PGA enhanced soil hydrothermal salt conditions. • γ-PGA improved cotton biomass, yield and fiber quality. • γ-PGA rate of 22.08 kg ha −1 was recommended as an appropriate strategy.