【Objective】The objectives of this study are to explore the response mechanism of citrus yield, quality and water-nitrogen use efficiency to water and nitrogen under surge-root irrigation in western Hubei, and to propose a water-nitrogen management mode for high-quality and high-yield of citrus, so as to provide a theoretical basis for the scientific management of water and nitrogen in citrus industry.【Method】6a-old Newhall navel orange was used as the test material, and the surge-root irrigation technology was adopted, and two factors of irrigation and nitrogen application were established. The two irrigation levels were full irrigation (FI: 70%-85%θf, θf is the field water holding capacity) and deficit irrigation (DI, 70%FI), and the three nitrogen application levels were high nitrogen (NH: 300 kg·hm-2), medium nitrogen (NM: 225 kg·hm-2) and low nitrogen (NL: 150 kg·hm-2), respectively. The effects of different water and nitrogen treatments on the yield, fruit quality and water-nitrogen use efficiency of citrus in western Hubei were analyzed, and the yield, quality and water-nitrogen use efficiency of citrus were comprehensively evaluated based on the game theory combination weighted TOPSIS method.【Result】Irrigation and nitrogen application under surge-root irrigation had significant effects on yield, single fruit weight, irrigation water use efficiency (IWUE), nitrogen partial factor productivity (NPFP), fruit diameter and fruit quality of western Hubei citrus (P<0.05). Moderate deficit irrigation and reduced nitrogen application were beneficial for improving the yield, quality and water-nitrogen utilization efficiency of citrus fruits. Among the treatments, the yield, single fruit weight, IWUE, fruit transverse and longitudinal diameter of DINM treatment were the largest, which were 24 458.38 kg·hm-2, 311.45 g, 40.48 kg·m-3, 89.02 mm and 87.18 mm, respectively. This represented an increase of 2.26%-25.66%, 1.92%-16.04%, 2.82%-78.46%, 8.85%-20.74%, and 3.33%-17.76% compared to other treatments. However, the DINL treatment exhibited the highest NPFP at 143.80 kg·kg-1. Under deficit irrigation conditions, the fruit moisture content was lower than that under full irrigation; however, the fruit hardness, soluble solid content, soluble reducing sugars, titratable acidity, vitamin C content, edible rate, and sugar-acid ratio were higher than those under full irrigation. Under full irrigation, the soluble solid content, soluble reducing sugars, vitamin C content, and sugar-acid ratio decreased with the reduction of nitrogen application. Compared with the FINH treatment, the FINM treatment decreased by 8.01%, 12.06%, 7.70%, and 14.55%, respectively, while the FINL treatment decreased by 14.97%, 18.19%, 10.54%, and 16.25%. Under deficit irrigation, the fruit moisture content, soluble solid content, soluble reducing sugars, titratable acidity, vitamin C content, edible rate, and sugar-acid ratio showed a trend of first increasing and then decreasing with the reduction of nitrogen application. Compared with DINM treatment, the DINH treatment decreased by 1.63%, 6.75%, 13.65%, 6.35%, 8.04%, 4.11%, and 9.18%, respectively, and the DINL treatment decreased by 3.30%, 14.55%, 20.55%, 4.76%, 10.98%, 7.50%, and 10.25%, respectively. The comprehensive weights of indexes were determined based on the game theory combination weighted TOPSIS method. The comprehensive weights of citrus yield, NPFP, IWUE and fruit quality were 0.399, 0.153, 0.104 and 0.344, respectively. The comprehensive evaluation results showed that the comprehensive score of DINM treatment was the highest, followed by DINH treatment, and the score of FINL treatment was the lowest.【Conclusion】The optimal water-nitrogen coupling mode of citrus in western Hubei under surge-root irrigation is 70%FI (FI: 70%-85%θf) and NM (225 kg·hm-2).
