Complementarity and competitive trade-offs enhance forage productivity, nutritive balance, land and water use, and economics in legume-grass intercropping

Legume-grass intercropping is proposed as a globally sustainable approach to enhance forage crop productivity and quality while supporting agropastoral ecosystem functioning. However, the mechanism involved in interspecific complementarity and competition driven forage productivity, quality, resource utilization, and economic benefits across different proportions of intercrops remains unclear, particularly under interannual climate variability. To address this, a 3-year field experiment was conducted in the agropastoral area of the Qinghai-Tibet Plateau (QTP) to assess the effects of different legume proportions (five legume-grass intercropping and their respective monocultures) and growing seasons on the productive, biological and economic viability. The results showed that legume proportions of 40 % and 50 % achieved the highest forage yield, system productivity (SP), water use efficiency (WUE), land equivalent ratio (LER), net profit (NP), return on investment (ROI), biodiversity effect (NE), and complementarity effect (CE) compared to other intercropping and monocultures (P < 0.05). As the legume proportion increased, yield stability, selection effect, crude protein (CP) and ash contents, grass aggressivity and competitive ratio significantly increased (P < 0.05), while ether extract (EE), crude fiber (CF), nitrogen-free extract (NFE), gross energy (GE), legume aggressivity and competitive ratio significantly decreased (P < 0.05). Additionally, the lowest forage yield, SP, NP, ROI, CP, EE, NFE, GE, and the highest WUE, LER, NE, CE, CF and ash contents were observed during the dry season (P < 0.05). Overall, our results suggested that the optimal legume proportions of 40–50 % increased forage productivity, land and water use efficiency, and economic benefits in intercropping system by improving complementarity and competitive trade-offs, which helps the intercropping systems better adapt to climatic droughts in the semiarid regions of the QTP.