Evaluation of Soil Quality and Cotton Productivity in Long-Term Cultivated Fields in the Southern Xinjiang Oasis

To investigate the effects of long-term cultivation on soil physicochemical properties, cotton production and soil quality dynamics in the oases of southern Xinjiang, uncultivated and unfertilized wasteland was used as the control (CK), and cotton fields with cultivation durations of 7, 12, 21, 30 and 40 years were selected in the Tailan River oasis. Soil physicochemical properties (0–200 cm) and cotton production indicators were measured. A minimum dataset (MDS) and soil quality index (SQI) were constructed, and obstacle-factor diagnosis, partial least-squares structural equation modelling (PLS-SEM), the Mantel test and multiple linear regression were used to identify key drivers. The results indicated that the SQI in the 0–40 cm soil layer showed an increase-then-decrease pattern with different cultivation histories. Organic matter (OM), available phosphorus (AP), pH and electrical conductivity (EC) were identified as major obstacle factors for SQI improvement. PLS-SEM indicated a strong positive association between soil nutrients and SQI, whereas salinity and alkalinity were negatively associated with SQI; cultivation duration was indirectly associated with SQI through its positive association with soil nutrients. Soil nutrients also had the strongest positive association with cotton yield, whereas salinity and alkalinity were negatively associated with yield. Reproductive organs’ dry weight (RDW), available potassium (AK) and OM were the most important predictors of cotton yield. In summary, the SQI showed an increase-then-decrease pattern across sampled fields with different cultivation histories, with the highest mean in 30-year fields and a lower mean in 40-year fields. Insufficient soil nutrient supply emerged as the primary obstacle to SQI and yield in long-term cultivated fields. Synergistic improvements in cotton yield and SQI can be achieved through measures such as optimising the combined application of nitrogen and phosphorus, regulating water and salinity, increasing the application of organic fertiliser and implementing appropriate crop rotation, thereby providing a reference for soil quality management and sustainable agricultural development in arid regions.