Legume-grass mixture synergistically boosts production, water use, and resilience in water-stressed artificial grasslands

Amid global climate change and water scarcity, enhancing water productivity while maintaining ecological sustainability in arid artificial grasslands is vital for regional water-forage-livestock system stability. However, how water management and biological interactions synergistically improve system resilience and resource efficiency remains unclear. This study aimed to evaluate whether legume-grass mixture combined with mild deficit irrigation could improve soil water and nutrient conditions, forage productivity, and water use efficiency. A three-year field experiment was conducted with three deficit irrigation levels (full irrigation (W0: 75%–85% θf), mild water deficit (W1: 65%–75% θf), moderate water deficit (W2: 55%–65% θf), where θf is field capacity) and three planting patterns (alfalfa monoculture (A), Bromus inermis monoculture (B), and alfalfa-Bromus inermis mixture (M)). Results showed that soil water content decreased with increasing deficit, but the mixture buffered moisture fluctuations and promoted soil organic matter accumulation under W1, while also alleviating photosynthetic inhibition. Compared with A and B monocultures, the mixture increased average yield by 5.13%–10.61% and 133.56%–137.39%, respectively, with land equivalent ratios exceeding 1.0 under all water regimes. Yield reduction under W1 was relatively small, while water use efficiency (WUE, FWUE, CPWUE) was significantly improved; the mixture increased average WUE by 12.86%–28.44% over A monoculture. W1 also enhanced crude protein content and relative feed value, with the mixture showing superior overall forage quality. Partial least squares path modeling indicated that water deficit and planting pattern primarily regulated yield and water productivity indirectly through soil water‑nutrient status and physiological processes. Comprehensive entropy weight‑TOPSIS evaluation showed that legume‑grass mixture under mild deficit (MW1) synergistically achieved water savings, soil fertility improvement, stable yield, quality enhancement, and increased efficiency, providing a theoretical basis for sustainable artificial grassland production in arid regions.