Assessing trade-offs among productive, economic, and environmental indicators of forage systems in southern Tibetan crop-livestock integration

Fostering crop-livestock integration via crop-forage rotation provides opportunities to cope with land degradation, feed deficit, and agropastoral sustainability. Farmers' preferences for forage options are influenced by economic benefit, environmental preference, and productive performance. However, there is little information available on evaluating multiple trade-offs of forage systems for the design of crop-forage rotations. Here, we performed a comprehensive evaluation to compare the economic, environmental, and productive indicators of five typical forage systems in terms of habitat conditions, soil ecosystem services, economic profit, and forage yield and nutritive value on the southern Tibetan Plateau. Alfalfa pasture and silage corn were mostly cultivated in lower altitudes, with more abundant precipitation, and higher growing degree days. Soil carbon and nitrogen accumulation were significantly higher in perennial alfalfa than in the other forage systems. The relative feed value of alfalfa pasture was also evidently greater than the other forage systems, whereas the yield of silage corn was among the highest. Alfalfa pasture presented superior economic benefits compared to the others. But the alfalfa pasture over six years showed a significant decrease in soil carbon and nitrogen storage, net present value, and yield. Forage systems generally have more soil carbon accumulation, but only forage legumes are more likely to positively affect soil nitrogen retention compared to cereal croplands. The trade-offs among economic, environmental, and productive indicators demonstrated that annual forage systems (silage corn, forage oat, and ryegrass) met productive target rather than environmental and economic objectives, while perennial alfalfa showed synergies among the three goals. These findings indicate that integrating crop-forage rotation, particularly introducing legume forages into farming systems is an adaptive option for crop-livestock integration on the southern Tibetan Plateau. Given the large topographic variation, suitable crop-forage systems should be designed for the heterogeneous Yarlung Zangbo River valleys. Among them, alfalfa-silage corn intercropping is recommended as a promising system to meet both productivity and profitability.