Water and nitrogen management strategies for stable-yield cotton in Northern Xinjiang under reduced nitrogen conditions

Currently, cotton production faces challenges such as excessive nitrogen fertilization and water scarcity, which affect yield, quality, and environmental sustainability. Adequate water and nitrogen supply was shown to enhance cotton growth, and moderate nitrogen application could partly offset yield losses caused by water deficit. However, nitrogen rates above critical thresholds led to diminishing returns, while excessive water and nitrogen inputs reduced water use efficiency (WUE) and nitrogen partial factor productivity (NPFP, kg kg−1). A synergistic effect on NPFP was observed between irrigation quota and nitrogen application rate, with a 10 % reduction in irrigation quota under conventional nitrogen use significantly improving WUE, and marked regulatory effects of irrigation on NPFP under low-nitrogen conditions (N4). To verify these findings, three irrigation regimes（W1:488 mm、W2:444 mm、W3:400 mm）and four nitrogen fertilization levels（N1:440 kg ha−1、N2:387 kg ha−1、N3:336 kg ha−1、N4:294 kg ha−1）were established in field experiments from 2022 to 2023. Three evaluation methods—principal component analysis (data dimensionality reduction), entropy-weighted TOPSIS (comprehensive ranking), and grey relational analysis (correlation analysis)—were applied to nine indicators covering irrigation cost, agronomic traits, and economic returns. The results indicated that an optimal combination of 400–444 mm irrigation quota with 387–440 kg ha−1 nitrogen application is suitable for Northern Xinjiang under film-mulched drip irrigation, supporting nitrogen reduction strategies while sustaining yield. This study provides a theoretical basis and technical framework for improving water–nitrogen resource efficiency and promoting sustainable cotton cultivation in arid regions.