Under-trellis cover crop and deficit irrigation to regulate water availability and enhance Tannat wine sensory attributes in a humid climate

The goal of our study was to improve Tannat grape and wine composition by achieving vine balance in high capacity conditions. The current Uruguayan grape-growing paradigm accepts unpredictable periods of water deficit or excess in non-irrigated vineyards, only applying herbicides to eliminate weed competition (H). We used an under-trellis cover crop (UTCC) to limit vine water availability and to reduce vine growth rate and final canopy size. However, to avoid excessive vine water stress due to UTCC competition, irrigation was used as needed during water deficit periods. The experiment was conducted over three consecutive growing seasons from 2011 to 2013, in two experimental vineyards located in southern Uruguay (34 degrees S 56 degrees W). Treatments were: UTCC (full cover of the vineyard soil with tall fescue) versus conventional alleyway tall fescue with a 1.0 m-wide weed-free strip under the trellis. Deficit drip irrigation was provided at mid-day stem water potential (SWP) thresholds of -0.9 MPa early in the season and -1.1 MPa later. Shoot growth rate, SWP, berry size and berry composition (Brix, organic acids, total anthocyanins) were monitored over the season as well as final yield, cluster and pruning weights and wine sensory attributes. UTCC regulated vine vegetative growth and final canopy size and reduced bunch rot incidence as well as increasing fruit Brix and anthocyanin concentration in grapes and wines. Wines from UTCC treatments had an increased fruity aroma and overall aroma intensity levels and had distinctive sensory characteristics that exceeded those of H wines during overall palatability tests (liking tests).