## 5 Conclusions and Implications  
This study revealed optimized intercropping systems of cultivated pastures in the mountain-basin systems of northwest China. We found that alfalfa-annual grass intercropping tended to increase the production ability and ecological functions in the MBS. The plant traits of alfalfa in mixtures were determined by variety at the earlier stage and affected by the companion grass at the later growth stage. Forage grasses inhibited the performance of alfalfa in mixtures in comparison with monocultures, and sudangrass displayed a stronger inhibiting effect than oat. The suppression by grasses impaired the growth of alfalfa in terms of plant height, branch number, light reception and biomass accumulation. Although the suppression effect of weeds tended to rise with time, alfalfa-grass intercropping enhanced the resistance to weeds compared with monocropping. The results advance our understanding of the growth responses of alfalfa to intercropping during the first growing season in arid regions and provided insights into interspecific interactions between alfalfa and annual forage grass. In conclusion, the promotion of combining alfalfa and annual forage grass, especially sudangrass, on small-hold farms in the MBS is advocated. This alternative strategy shows not only yield advantages over monocrops but also ecological benefits to preserving natural pastures in the MBS.  
Companion crops such as oat and sudangrass increased the forage yield of alfalfa pastures in the first year. In our study, alfalfa-grass intercropping was proven to be a promising cropping practice to prevent weed infestation. Therefore, based on the current cropping system, from the perspectives of yield, production stability and weed control, planting the variety leafy king or WL354 HQ with sudangrass could be considered as a strategy to balance the goals of forage yield and ecological functions of cultivated pastures in the MBS (Figure A4). However, the results could vary under dissimilar field conditions, such as soil properties and local climate disturbance. Adequate irrigation as well as grazing exclusion should be taken into account in agronomic management. To obtain better alfalfa-grass intercropping systems in the MBS, future studies should focus on the effects of various sowing ratios and other companion grass species.  
Conceptualization, Y.F., B.L. and L.M.; validation, X.D. and X.B.; formal analysis, Y.F. and X.T.; investigation, Y.F., X.D. and L.M.; data curation, Y.F. and X.D.; writing--original draft, Y.F.; writing--review and editing, Y.F. and B.L.; visualization, X.T. and Z.Y.; project administration, Y.F.; funding acquisition, B.L.; supervision, B.L. and X.Z. All authors have read and agreed to the published version of the manuscript.  
This research received financial support from the National Natural Science Foundation of China (No. 42071228) and the National Science and Technology Planning Project of China (No. 2014 BAC15B04).  
**Acknowledgments:** The authors acknowledge the support of the Fuyun Grassland Station and the government of Dure Town for providing the demonstration field and helping with the agronomic management. We would like to thank [PERSON] and [PERSON] for their help with the field work.  
**Conflicts of Interest:** The authors declare no conflict of interest.