Combination of cover crops and microbial biostimulants: Impacts on soil functioning, grape production, and juice quality in rainfed vineyards

Vineyards are intensively managed agroecosystems, which can reduce their soil functioning and biodiversity, with consequences for grape and wine quality. New regulations (e.g., Europe’s green policies) and market demand for environmentally respectful products are encouraging the adoption of a range of nature-based practices such as cover crops and microbial biostimulants, yet their combined effects remain poorly evaluated. We conducted a fully factorial field experiment in rainfed vineyards in southern Spain to assess the simultaneous effects of two sustainable management strategies: the use of winter cover crops, as opposed to year-round tillage, and the foliar application of a nitrogen-fixing microbial biostimulant at two doses (1x and 3x based on the recommendations of the manufacturer). Cover crops increased the activity of soil extracellular enzymes associated with the C, N and P cycles, indicating enhanced decomposition potential, whereas the biostimulant did not consistently alter soil enzyme activity. Across two seasons, cover crops slightly reduced yield, but this effect was non-significant, while the biostimulant increased production in the first vintage. Importantly, the combination of cover crops with a high biostimulant dose achieved yields comparable to, or even higher than, tilled controls. The combined treatments suggested potential synergistic responses in ºBrix (indicative of total soluble solids) and pH of musts. Using structural equation modelling, we provided additional mechanistic evidence that cover crops and microbial biostimulants are two compatible strategies that may enhance, through complementary mechanisms (i.e., promoting either soil or plant health), the sustainability of vineyards. Our findings support the combination of these practices as a viable pathway toward more resilient and environmentally respectful viticulture.