Biofertilizer application alleviates salt stress and improves yields in saline water drip-irrigated cotton fields in South Xinjiang, China

The use of saline water for irrigation offers a sustainable solution to freshwater scarcity in arid regions, but salt stress from saline water negatively impacts cotton growth. In 2021 and 2022, a two-year study was performed on film-mulched drip-irrigated cotton fields in Southern Xinjiang, China. The study aimed to evaluate how biofertilizer (F 2 ) affects soil moisture, soil salinity, cotton plant ionic homeostasis, and crop yield under varying salinity conditions of irrigation water. Salinity levels tested were 0.48 −1 g L −1 (W 1 , freshwater), 3 g L −1 (W 2 , brackish water), and 7 g L −1 (W 3 , salt water), in comparison with chemical fertilizer (F 1 ) application alone. The results showed that biofertilizers effectively increased water content in the 0 −40 cm soil layer and reduced salt accumulation within this zone in cotton fields. This process effectively balances soil salt ions, lowers Na + and Cl − concentrations in the 0 −60 cm soil depth, and increases K + and HCO 3 − levels. Furthermore, biofertilizer application reduced Na + and Cl − uptake by cotton plants while enhancing K + absorption, thereby altering the plants’ ionic composition. This led to a significant increase in K + /Na + and Ca 2+ /Na + ratios under brackish and saline irrigation conditions, mitigating the negative effects of salinity stress on crop growth. Partial least squares analysis confirmed that biofertilizers effectively decreased soil salts and salt ions, reduced plant uptake of harmful ions, and improved ionic homeostasis, contributing to higher seed cotton yields. Compared to the F 1 (W 1 F 1 , W 2 F 1 ) treatments, seed cotton yields in the F 2 (W 1 F 2 , W 2 F 2 ) treatments increased by 6.15%−10.56% (W 1 F 2 ) and 6.49%−11.80% (W 2 F 2 ) over two years. However, the yield increase was less pronounced under saline water irrigation. This research provides new insights for reducing salt stress in crops and for the secure use of saline water in agricultural irrigation.