Developing diversified forage cropping systems for synergistically enhancing yield, economic benefits, and soil quality in the Yangtze River Basin

Crop diversification represents a promising pathway towards sustainable farming system. In order to address the severe constraints imposed on agricultural and livestock development due to the scarcity of high-quality forage in the Yangtze River Basin, we employed the principles of crop diversification to enhance crop diversity and intensification at both spatial and temporal scales through intercropping and crop rotation. We developed five diversified double cropping systems: rapeseed-maize, barley-maize, hairy vetch-maize, rapeseed/hairy vetch intercropping-maize, and barley/hairy vetch intercropping-maize. Using a long-term experiment established in 2017, we investigated the intercropping effects of winter crops on biomass production, their legacy effect on soil quality, root and canopy traits, weed occurrence, forage and protein yield of subsequent maize, as well as the economic benefits, covering the period from 2019 to 2021. We found that intercropping, compared to sole cropping, significantly increased winter forage yield by 9.7–136.3%. Furthermore, it significantly improved soil fertility and enhanced soil structure and the activity of nutrient cycling-related enzymes. Such legacy effects further promoted root biomass, activity, and morpho-physiological traits of subsequent maize, facilitating canopy development and leaf photosynthesis, reducing weed occurrence, and increasing summer forage yield by 24.9–27.1%, albeit slightly lower than the yield of maize following hairy vetch. Remarkably, the rapeseed/hairy vetch intercropping-maize system showed the highest annual biomass (39.9 Mg ha−1) and crude protein (5.18 Mg ha−1) yield, leading to a net profit value increase of 67.1–80.7%. In conclusion, diversification through intercropping and rotation enhanced the crop-soil interactions and positive feedbacks, ultimately improving system productivity and economic benefits, proving to be an innovative and sustainable approach for promoting forage production in the Yangtze River Basin and beyond.