Cover crops drive soil carbon retention in semi-arid sloping vineyards

Background: Soil organic carbon (SOC) is essential for maintaining soil health, contributing to fertility, structure, and climate change mitigation. In semi-arid vineyards, however, its preservation is increasingly challenged by erosion and unsustainable practices such as conventional tillage. The use of cover crops has been proposed as a sustainable strategy to improve soil quality; however, in semi-arid environments, this approach presents a trade-off. While it can enhance soil structure and organic matter, as well as reduce soil erosion, it may also increase water loss through evapotranspiration, potentially reducing yields. This study explores how slope-driven erosion and soil type interact with management practices to shape the mechanisms of SOC stabilization and depletion. Results: We demonstrate that cover crops mainly act by reducing erosion-mediated SOC loss, rather than by increasing SOC directly. This erosion-control mechanism is especially effective on steep slopes (length-steepness factor (LS) > 1.15), where SOC losses under conventional tillage are greatest. Soils derived from marl show a higher carbon saturation deficit, indicating a greater potential for effective SOC retention. In contrast, flatter areas show minimal differences between cover crop and conventional management, suggesting limited SOC gains where erosion is not a major driver. Extending our results to the biggest island in the Mediterranean, we discovered that most of the vineyards (60.56%) fall in the zone with a flat slope, probably benefiting from not using the cover crop. Conclusions: The results suggest that a targeted approach to cover crop implementation, based on slope conditions, can maximize soil carbon benefits while minimizing potential drawbacks in semi-arid vineyards. By applying cover crops primarily in areas with higher erosion risk, farmers can enhance carbon storage and reduce soil degradation without compromising water availability for vines. This site-specific strategy provides practical guidance for vineyard soil management and can support more sustainable agricultural policies and practices in semi-arid regions.