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.