Soil Management Effects on Grapevine Water Uptake Depth in a Mediterranean Vineyard

In Mediterranean vineyards, soils are often managed with tillage or herbicides to limit weed growth and competition for resources. However, with rising concerns about water scarcity and climate change, cover crops are being reconsidered as sustainable alternatives to conserve soil moisture and support adaptation through better soil structure and biodiversity. Although they are often reported to decrease yields, this is not always the case, and the magnitude and timing of their competition for resources with vines are still not well understood. To address this gap, we examined vine and cover crop water uptake depth during veraison in August in a vineyard from Rioja Alavesa, Spain. We compared tillage (control treatment) with spontaneous cover crop. Using the isotopic composition of plant and soil water (δ 18 O and δ 2 H) and Bayesian mixing models, we found that the cover crop relied on water from the upper soil (100% from 0 to 30 cm), while vines under cover crop accessed water from shallow (~48% from 0 to 30 cm) and deeper soil layers (~52% from 30 to 100 cm). Despite cover crops and vines competing for water in the upper soil, the vine's ability to access water from both shallow and deeper soil horizons helped maintain its water status during veraison. Vines under tillage relied predominantly on water in the deeper soil (~73% from 30 to 100 cm). These results indicate that soil management strongly influences vine water uptake patterns. In our vineyard, the spontaneous summer cover crop did not compromise vine water availability during veraison.