Water and nitrogen application enhance eggplant productivity and nitrogen use efficiency in an arid environment

Water scarcity and excessive nitrogen fertilizer application are bottlenecks constraining the sustainable development of agriculture in the cold and arid Hexi Corridor region of China. However, the interactive effects of deficit irrigation and nitrogen rate on eggplant physiology, yield, and resource efficiency remain insufficiently quantified for this region, and the optimal water-nitrogen combination for practical application is unclear. To address this gap, a two-year field experiment was conducted with three water deficit levels (W0, full irrigation; W1, mild water deficit; and W2, moderate water deficit) and three nitrogen application rates (N1, low nitrogen application; N2, medium nitrogen application; and N3, high nitrogen application). Full irrigation without nitrogen application served as the control. Plant height, stem diameter, leaf area index, and dry matter accumulation (DMA) increased with increasing nitrogen application rates under the W0 and W1 levels. Appropriate water-nitrogen management enhanced DMA in fruits and improved individual fruit number and weight. The W1N2 treatment (soil moisture content at 60-70% field capacity and nitrogen application rate of 270 kg·ha^-1) achieved the highest yield, crop water productivity, and irrigation water productivity. Compared with the CK, the W1N2 treatment significantly increased (P < 0.05) yield, crop water productivity, and irrigation water productivity by 32.62%, 37.84%, and 38.33% in 2021, and by 35.06%, 42.48%, and 45.53% in 2022, respectively. The N3 treatment significantly reduced nitrogen partial factor productivity. In summary, the combination of mild water deficit and medium nitrogen application represents the optimal water-nitrogen management strategy for eggplant production in the Hexi Corridor. This study offers theoretical and technical support for water and nitrogen conservation in sustainable eggplant production in arid regions.