Interrow cover crops in a semi-arid vineyard increase plant beneficial functional potential of the soil microbiome, both in vine rows and interrows, a benefit that increases with cover crop duration.

Background: Cover crops are recognized for enhancing soil health and providing agroecosystem services, but are not widely adopted, particularly in water-limited regions. In Mediterranean vineyards, where water scarcity and soil degradation challenge productivity, interrow, cool-season cover cropping offers a promising strategy to improve microbial-mediated soil functions. However, the temporal and spatial effects of cover crops on vineyard soil microbiomes and soil health metrics remain poorly understood. This study evaluated the impacts of a California native (phacelia, Phacelia tanacetifolia) and introduced (rye, Secale cereale L.) plant species as interrow cover crops on soil properties in interrow and vine row soils across three years.

Results: The study revealed distinct temporal and spatial dynamics in soil microbiomes elicited by the cover crop treatments. By the third year, phacelia exhibited the highest microbial biomass, fungal-to-bacterial ratios, and microbial network complexity. Interrow soils showed stronger responses to cover cropping, including enhanced microbial biomass and differentiation between treatments, while vine row soils demonstrated subtler but significant shifts in microbial metrics. Functional predictions indicated that cover crops reduced fungal pathogen prevalence and supported nutrient cycling processes. Deterministic processes driven by environmental selection became dominant under both treatments, promoting microbial resilience. Random Forest analysis identified NO₃^- as a key driver of microbial differentiation, with phacelia fostering communities reliant on labile organic inputs.

Conclusions: This study highlights a crucial benefit of interrow cover crops in improving soil health and enhancing microbial-mediated ecosystem functions in adjacent vine row soils, even after cover crop termination. Long-term application of cover crops offers a sustainable approach to building resilient agroecosystems in water-scarce environments, with implications for sustainable viticulture practices.