Abstract: Abstract：Nitrogen is a main nutrient element for crop growth but the appropriate nitrogen application and management isimportant in the Yellow River Irrigation Area of Ningxia. So, an effective method of accurate nitrogen assessment for maize isurgently needed in this area. In this study, based on leaf area index (LAI) of maize under drip-irrigated system, a criticalnitrogen dilution curve model was established and its applicability for nitrogen management was assessed. The feasibility ofdiagnosing nitrogen nutrition status of maize under a water and fertilizer drip-integrated mode by using nitrogen nutritionindex (NNI) was also evaluated. Six nitrogen application rates with three replicates each were designed including 0 (N0)、90(N90)、180 (N180)、270 (N270)、360 (N360), and 450 (N450) kg/hm2 in 2017 and 2018. The LAI, dry matter and nitrogenconcentration were determined at jointing stage, trumpet stage, large trumpet stage, tasseling stage, and silking stage,respectively. Then, the quantitative relationship between LAI and plant nitrogen concentration (PNC) were analyzed.Moreover, the critical nitrogen dilution curve model based on LAI was constructed and verified after analysis of aboveground biomass accumulation and plant nitrogen concentration of maize from jointing stage to silking stage under differentnitrogen application rates. The critical nitrogen dilution curve model was employed to reveal the effects of nitrogenapplication rates on NNI of maize at different growth stages. A theoretical framework was established to reveal therelationship between LAI and plant dry matter (PDM) curves and to compare the differences between critical nitrogen curvebased on LAI and that based on PDM. The results showed that, as a whole, both LAI and plant nitrogen concentration wereincreased as nitrogen application rate increased. However, they increased with two distinct periods, which could be classifiedinto nitrogen limitation and nitrogen non-limitation periods. The relationship between critical nitrogen and LAI conformed toa power function model at the vegetative growth stage of maize. Meanwhile, the root mean square error (RMSE) andnormalized root mean square error (n-RMSE) of this established model were 0.09 and 4.13%, respectively. It indicated thismodel presented a good stability to predict critical nitrogen concentration of maize as well as to evaluate plant nitrogennutrient at the vegetative growth stage. Furthermore, the NNI increased from 0.53 to 1.34 when the nitrogen fertilizerapplication rate increased at different growth stages. Hence, NNI could accurately reflect the nitrogen nutrition status ofmaize, and 270 kg / hm2 was the best application rate of nitrogen in this study. In addition, under non-limited nitrogencondition, the nitrogen absorption of maize plants presented a positive correlation with LAI and the allometric growthparameters of LAI and PDM were closer to two thirds of the theoretical value. In conclusion, the established critical nitrogencurve based on LAI can effectively identify the nitrogen condition required by the plant from the jointing stage to the silkingstage. The critical nitrogen curve based on leaf area index provides an effective evaluation method for precise nitrogenmanagement of maize under drip-irrigated system in Ningxia.