## 1 Introduction  
Overgrazing and the degradation of natural grassland have been inevitable and represent constraints on husbandry development in the arid regions of northwest China [1]. Changes in grazing regimes, such as grazing exclusion and rotational grazing, have limitations in the conservation and restoration of natural grasslands. The typical vast compound landforms including mountain, oasis and desert in this region were defined as mountain-basin systems (MBS) by [PERSON] [2]. The MBS comprises interacting subsystems with the exchange of energy, material, life and culture [3]. Cultivated pasturesin oasis areas were regarded as an essential component of the eco-productive paradigm for ecological restoration and sustainable development in the MBS. Cultivated pasture is also regarded as a proper strategy of restoration for degraded grasslands by carbon sequestration and nitrogen assimilation [4]. Planting forage is an effective method to improve primary productivity [5], thus mitigating grazing pressure on natural grasslands. A low-input forage-based system on small farms with suitable production capacity is essential to improving livestock production and herdsmen's livelihoods. Alfalfa, or lucerne, is a widely grown perennial legume forage well adapted to drought and can survive extreme environments [6]. In the oasis areas of northern Junggar Basin, alfalfa is currently sown in monocrops for forage production by small-scale herdsmen in a maize-alfalfa rotation system with the utilization of silage or fodder. In arid regions, cultivated pasture is an important support system for the conversion of nomadic livelihood to household settlement, which contributes to labor force liberation. However, the weak growth of alfalfa in the first year leads to a low yield and shortage of forage in autumn and winter [7]. Hence, considering forage production and ecological preservation, there is an urgent need to alter the existing cropping system to develop better intercrop regimes. Studies on diversified cropping systems and species interactions have been considered as ways to understand how functional diversity affects ecosystem functions and services [8]. The exploration of designing plant communities not only enriches theoretical knowledge about the interactions between plant species but also provides effective functional groups and practical ecosystem management [9]. Intercropping is considered a small-scale potential agricultural land use pattern and arranged combinations of species to develop sustainable agroecosystems by improving land-use efficiency [10]. Increased plant species richness often facilitates productivity, stability, invasion resistance and reduces vulnerability to environmental disturbance [11; 12]. Reasonable species configurations and agronomic management result in the high productivity and stability of the agroecosystem [13]. However, designing intercropping systems is complex because of the uncertain interactions between component species, preferences of the local community and the available management practices [14]. Reduced yield may be possible due to the inappropriate arrangement of the component crops and unreasonable practical management. Complex mixtures are not necessarily yielding more than binary mixtures [15]. Thus, the selection of species and proper arrangements for seeding ratios for small households are essential for an efficient intercropping system to capture a greater range of resources. Planting legumes has been regarded as an important way to promote sustainable and environmentally friendly agricultural practices to meet the growing needs for food and forage production because of the foreseeable rising world population [16]. Legume-grass intercropping is a valuable sowing regime for overyielding because of the niche differentiation in plant traits and resource acquisition [17; 18].