Abstract:In response to the problems of natural grassland degradation, serious soil erosion, and low productivity of artificial grassland in arid steppe region of Northwest China, effects of planting patterns, water and nitrogen regulation on forage yield, quality and water and nitrogen use efficiency were investigated in order to obtain a high-yielding and high efficiency grassland management pattern. In this study, triennial alfalfa and Bromus inermis (sown in 2018) were used as experimental materials to analyze planting patterns (mixed alfalfa and B. inermis, unicasted B. inermis; namely D1, D2), the amount of nitrogen application (N 60 kg/hm2, 120 kg/hm2; namely N1, N2), and irrigation water gradient (calculated by the percentage of irrigation water limit to the field water holding capacity, light deficit 65% θf, moderate deficit 55% θf, severe deficit 45% θf, recorded as W1, W2, W3, the upper limit of irrigation is 85% θf) on forage yield, quality and water and nitrogen use efficiency. The results showed that:(1)Increasing irrigation amount and nitrogen application rate was beneficial to the growth of plant height and stem diameter. Compared with W3N1 treatment, the average plant height of mixed alfalfa and B. inermis, unicasted B.inermis increased by 27.41% and 20.26%, 26.55%, and stem diameter increased by 11.32% and 4.11%, 20.98% under W1N2 treatment, and mixed forage had a promoting effect on B. inermis plant height and a suppressing effect on stem diameter. (2) The increase of irrigation amount and nitrogen application rate was beneficial to improve the forage yield and quality. The annual yield and crude protein (CP) content of forage under W1N2 treatment were the highest, and compared with W3N1 treatment, the annual yield and CP content of mixed forage increased by 42.16% and 27.00%, and unicasted forage increased by 38.59% and 37.26%. Respectively, ADF and NDF of mixed forage decreased by 19.56% and 33.86%, and unicasted forage decreased by 21.29% and 25.53%. (3) With the increase of irrigation amount, IWUE and WUE decreased, while PFPN increased. With the increase of nitrogen application rate, IWUE, WUE and PFPN decreased in mixed forage, while IWUE and PFPN decreased and WUE increased in unicast forage. Based on the principal component analysis, the highest combined score of light deficit (irrigation lower limit:65% θf) and high nitrogen (120 kg/hm2) was obtained in the mixed forage, which was a suitable water and nitrogen management pattern in the region. This result can provide a theoretical basis for forage planting management in arid and semi-arid grassland region of Northwest China.