Impact of crop load on yield, and berry and wine composition of cv. Bonarda, Mendoza

Abstract

Production of high quality grapes requires balanced vines, assessed through leaf to fruit ratio or Ravaz Index (RI). In some areas with high yield potential, canopy management is used in vineyards to increase yields to profit from this potential. One way is to increase number of shoots per m of canopy. In vertically shoot positioned trellising systems (VSP), this may lead to excessive shading in the cluster zone and to a high RI value during the first year. In the mean and long term, fertility may be affected by microclimatic conditions. Our aim was to evaluate the impact of shoot number on berry and wine composition in a region with high yield potential. The experiment was carried out in a vineyard (cv. Bonarda) trained to VSP, located in Rivadavia (Mendoza). Treatments corresponded to two levels of shoot number per plant: Control (C) and thinned (T) with 20 and 12 shoots per plant, respectively. These treatments corresponded to 15 and 9 shoot m^-1 of canopy. Shoot thinning was performed early in the season. Treatments were replicated 6 times each in a completely randomized design. Pruning weight and yield components were evaluated and wines made. Berry and wine composition were analyzed. The results showed that yield decreased by 40% in thinned plants, due to a reduction in the number of clusters per plant. Sugar maturity was achieved at the same time by the two treatments. No differences were observed in berry and wine pH, acidity, IPT, or anthocyanin content, probably because there was no modification on cluster microclimate. Our preliminary results after one year of study suggest that shoot thinning in a high yield potential vineyard does not improve vine balance or increase grape quality. However, more years of study are necessary in order to assess the impact of shoot number in the long term. Other management practices would most likely be more efficient.