Impact of Cultivation Practices in Oasis Agriculture on Soil Fertility Dynamics and the Relationship with Cotton Nitrogen-Use Efficiency in the Southern Rim of the Tarim Basin, Xinjiang, China

Twenty croplands in the Cele Oasis, at the southern margin of the Tarim Basin of Xinjiang, representing 100, 80, 30, 15, and 10 years of cultivation, were selected to investigate the relationship between soil fertility and nitrogen-fertilizer-use efficiency (NUE) of cotton and its changes over time. After long-term cultivation, significant increases were observed in soil organic matter (SOM) and total macronutrients. The key factors contributing towards the soil fertility index (SFI) were SOM, available potassium (AK), and phosphorus. The values of SFI declined in the following order: 80 (0.95) > 100 (0.68) > 30 (0.43) > 15 (0.41) > 0 (0.37) > 10 (0.34) years. No significant relationship was found between SFI and NUE. A significant correlation was observed among cotton yield, partial factor productivity from applied N, and AK. This indicates that the variation of AK content plays the most important role in soil fertility and cotton yield. Moderate K fertilization is recommended in the oasis croplands.