Cover Crops and Tillage in a Mature Merlot Vineyard Show Few Effects on Grapevines

Permanent cover crops are commonly used in vineyard floor management because of their beneficial effects to soil and vine health, but studies evaluating their competitive effects on vines have been conducted primarily in nonirrigated vineyards. Future air quality regulations could mandate the use of no-till floor management practices in California’s Central Valley. We evaluated the combined effects of cover crop type (oats alone or oats grown with legumes) and tillage on soil nutrient availability, vine nutrition, growth, and yield characteristics of Vitis vinifera cv. Merlot grown under regulated deficit irrigation in a commercial vineyard from 2008 to 2010. Five treatments were used: Resident Vegetation (RV) + Till, Oats + Till, Oats/Legumes +Till, Oats + NoTill, and Oats/Legumes + NoTill. No differences in soil nutrient availability were found among the treatments. Of the numerous nutritional constituents analyzed on leaf petioles and blades, only NO 3 -N petiole was affected by floor management. At nearly all growth stages among all years, NO 3 -N petiole of tilled treatments was twice the no-till treatments. At harvest, yield, mean cluster weight, cluster number per vine, and aboveground cover crop biomass differed among treatments in 2009 and/or 2010 but not in the first year (2008); however, responses were not consistent among treatments within each respective year. Importantly, yields were similar from all four cover crop treatments compared to the typical management (RV + Till), suggesting that use of cover crops and/or no-till practices may be implemented in an irrigated vineyard with little immediate effect on grape productivity in mature vineyards.