Abstract: [Objective] To explore the correlation among plant productivity, nutritional quality and soil physicochemical properties under different combined nitrogen and phosphorus applications in mixed grassland of Medicago sativa L. and Elymus sibiricus L. in arid and semi-arid regions of Inner Mongolia, and to screen the optimal fertilization ratio. [Methods] The arid and semi-arid regions of Inner Mongolia were selected, and the artificial grassland mixed with Zhongmu No. 3 M. sativa and E. sibiricus was used as the research object. Nine fertilization treatments were designed. Potassium （K） fertilizer was set at two gradients: 0 and 180.00 kg/hm², designated as K0 and K2, respectively. Nitrogen fertilizer was set at four gradients: 0, 146.67, 300.00, and 446.67 kg/hm², designated as N0, N1, N2, and N3, respectively. Phosphorus fertilizer was set at four gradients: 0, 266.67, 540.00, and 806.67 kg/hm², designated as P0, P1, P2, and P3, respectively. Each group was combined with different application rates of nitrogen, phosphorus and potassium to form a gradient experiment group. By measuring the plant productivity, nutritional quality and soil physicochemical properties, and analyzing the correlation between the indicators, a comprehensive evaluation was performed. [Results] ① Soil available nitrogen and available phosphorus were significantly positively correlated with the average height of plant communities, biomass and dry-to-fresh ratio （P<0.05）, significantly negatively correlated with the average stem-to-leaf ratio of the plant community （P<0.05）, significantly positively correlated with plant crude fat content and relative feed value （P<0.05）, and negatively correlated with neutral detergent fiber and acid detergent fiber （only the negative correlation between soil available nitrogen and neutral detergent fiber was not significant）.soil available phosphorus was extremely significantly positively correlated with plant crude protein （P<0.01）. ② Comprehensive evaluation using the entropy weight-TOPSIS model combined with grey relational analysis showed the fertilization effect was: N2P2K2>N2P3K2>N3P2K2>N1P2K2>N2P1K2>N0P2K2>N1P1K2>N2P0K2>N0P0K0. [Conclusion] It was preliminarily determined that N2P2K2 and N2P3K2 （the application rate of nitrogen fertilizer was 300.00 kg/hm², the application rate of phosphorus fertilizer was 540.00-806.67 kg/hm², and the application rate of potassium fertilizer was 180.00 kg/hm²） were the best fertilization ratios for legume-grass mixed grassland in arid and semi-arid regions of Inner Mongolia.

Key words: nitrogen and phosphorus addition ratio, legume-grass mixture, correlation analysis, comprehensive evaluation