Optimization of water and fertilizer management for apple (Malus pumila mill.) in the sandy regions of southern Xinjiang under organic fertilizer based on entropy weight-TOPSIS comprehensive evaluation

Apple orchards in the arid sandy regions of southern Xinjiang suffer from water scarcity, low soil fertility and soil structural degradation. Although organic fertilization can improve sandy soil structure and reduce dependence on chemical fertilizers, there are few multi‑year field studies in drip‑irrigated apple systems that simultaneously optimize water–nitrogen–potassium inputs with respect to yield, fruit quality, water–fertilizer use efficiency, and economic benefits. To address this gap, a three‑year (2021–2023) field experiment was conducted in a sandy apple orchard in southern Xinjiang under organic fertilization, using a quadratic orthogonal rotation design with three factors: irrigation amount (W), nitrogen amount (N), and potassium amount (K), each at five levels. To integrate yield, fruit quality, water–fertilizer use efficiency and economic benefits into a single decision index, we developed an entropy weight-TOPSIS comprehensive evaluation system combined with a water–fertilizer response model. With experiment progression, differences between organic fertilizer (OF) and the control (CK) became more pronounced. In 2022–2023, OF increased SPAD, leaf area index and new shoot length by 2.15%–4.36%, 4.50%–9.72% and 2.89%–5.91%, respectively, relative to CK. Apple yield increased by 4.24%–8.22%, while water use efficiency rose by 5.11% and 10.67%, and economic benefits by 3.89% and 6.29% in 2022 and 2023, respectively. Under WN, WK and NK interactions, OF increased the maximum comprehensive evaluation score by 4.43%–9.40%, 0.57%–9.60% and 1.88%–9.36%, respectively. Under three factor interaction, OF reduced optimal W by 2.44%–27.52% and optimal N by 19.26%–26.50%, while increasing optimal K by 11.19%–126.45%. The recommended optimal ranges under OF are W 591.81–600.33 mm, N 231.57–236.67 kg·ha⁻¹ and K 112.90–115.03 kg·ha⁻¹ , providing quantitative guidance for organic based precision water–fertilizer management in arid sandy apple orchards. • Organic fertilization improved apple yield, quality and water-use efficiency in arid sandy orchards. • Entropy-weighted TOPSIS-response models integrated indices and optimized W–N–K inputs. • Organic fertilization improved water–fertilizer coupling, enabling lower irrigation and nitrogen rates for sustainability.