Performance of Mencía grapevine cultivar under different soil management treatments

Abstract

Vineyards are usually managed using tillage to eliminate competition from other plants. However, this practice presents several drawbacks including degradation of soil structure, loss of organic matter and it may lead to considerable soil loss if the vineyard is on a slope. In addition, viticulturalists use herbicides for controlling weeds, with the consequent environmental drawbacks. On the other hand, vegetal ground covers may help reducing soil erosion and the use of pesticides. They also reduce vineyard vegetative expression since covers compete actively with grapevines for water and nutrients. In Galicia, red wines are mainly made from Mencía cultivar, which is highly productive, thus green prunings are needed for improving grape maturity. In this sense, this study aimed to assess the effect of several vegetal ground covers on the agronomic and enological response of Mencía cultivar. The experiment was carried out during 2012 on a rainfed Mencía vineyard located in the Estación de Viticultura e Enoloxía de Galicia (EVEGA) in Leiro (Ourense) within the D.O. Ribeiro. Soil at the experimental plot is an inceptisol with sandy-loam texture. During the season, from April to September, average temperature was 17.1 ºC and total rainfall amounted to 352.8 mm. The experimental design consisted of a control with tillage and three ground cover treatments: spontaneous vegetation, Lolium perenne and Trifolium subterraneum. Three replications for each treatment were considered. Plant water status was assessed through periodical measurements of stem water potential. Stomatal conductance was also determined at midday. Agronomic (number of clusters per plant, yield per plant, weight of 50 berries) and must and wine (alcohol content, pH, titratable acidity, tartaric and malic acids) parameters were measured. Although plants did not suffer from water stress under any of the considered treatments, those under tillage showed the less negative values of stem water potential. Stomatal conductance followed the same dynamics over the season for all the treatments. No significant differences in yield were detected; however, plants under tillage presented the highest yield value (2.5 kg/plant) and those under Trifolium the lowest one (1.95 kg/plant). Average cluster weight was greater under tillage (178 g) than under Lolium (138 g) or Trifolium (125 g). Musts and wine parameters were very similar for the different soil management treatments. However, musts from the treatments under Lolium and Trifolium presented lower probable alcoholic grades and were more acid (12.2 % volume and 4.6 g tartaric L^-1) than those under tillage or spontaneous vegetation (12.5 % volume and 4.2 g tartaric L^-1). In conclusion, vegetal ground covers did not compromise must and wine quality.