Combining Reduced Irrigation with Organic Fertilizer Substitution Enhances Water-Nitrogen Productivity and Soil Carbon-Nitrogen Pools of Maize in Arid Northwest China.

To address the challenges of excessive water and fertilizer application, declining soil fertility, and suboptimal maize yields in the oasis irrigation areas of Northwest China, a two-year (2024-2025) field experiment was conducted. Three irrigation levels were implemented: a 30% reduction (W1: 3575 m3·ha-1), a 15% reduction (W2: 4335 m3·ha-1), and conventional irrigation (W3: 5100 m3·ha-1). Nitrogen management comprised three strategies: 30% organic substitution (N3), 15% organic substitution (N2), and full chemical nitrogen fertilizer (N1). Statistical approaches, including correlation analysis and the CRITIC-AHP-VIKOR comprehensive evaluation model, were applied. The results indicated that ear length differed significantly among treatments, with the longest ears observed in W2N2 and W3N2 (17.39-17.68 cm) and the shortest in W1N1 (14.52 cm). Under W2 conditions, the kernel number per ear in N2 was 1.73% higher than that in N3, whereas under W1 conditions, N2 showed a 0.21% reduction compared to N3. The 100-kernel weight varied minimally, ranging from 32.04 to 40.70 g, with no significant difference between W2N2 and W3N3. Among all treatments, W2N2 produced the greatest yield, exceeding those of W3N3 and W2N3 by 6.07% and 5.96%, respectively. During the two experiments years, this treatment also promoted the accumulation of soil carbon and nitrogen in the 0-20 cm layer, increasing soil organic matter by 22.34-118.15% and total nitrogen by 5.62-40.45%. In contrast, grain quality parameters, including crude protein, crude starch, and crude fat contents, did not differ significantly between W2N2 and W3N3. Moreover, W2N2 achieved an irrigation water use efficiency of 4.41 kg·m-3, which was significantly greater than that under W1N2, while nitrogen use efficiency was improved by 42.57%. Correlation analysis revealed that maize yield is significantly positively correlated with soil carbon and nitrogen pools, grain quality indicators, and nitrogen fertilizer partial productivity, whereas quality parameters were positively correlated with irrigation water use efficiency, though not significantly. The CRITIC-AHP-VIKOR model identified that the comprehensive strategy of 15% irrigation reduction combined with 15% organic nitrogen substitution synergistically enhances maize yield, maintains soil carbon and nitrogen pools, and improves water-nitrogen use efficiency. These results provide a theoretical basis for promoting sustainable maize cultivation in arid irrigated areas characterized by limited water and nitrogen availability.