Foliar fertilization and bunch thinning of 'cabernet sauvignon' grapes

In wine grapes, bunch thinning at veraison is used to increase uniformity and quality of final product, at the expense of final yield. The aim of this study was to verify whether foliar fertilization could allow for quality improvements similar to those usually obtained with bunch thinning and at the same time maintain good yield. Three treatments were applied to non-fertilized and conventionally fertilized five-year-old spur-pruned vines of 'Cabernet Sauvignon', 1) a non-fertilized and non-thinned control (CTR), 2) a thinning treatment at veraison stage (TH), and 3) a foliar fertilization treatment with three applications starting after berry cell division phase (FOL). Yield of TH was lower than CTR and FOL, regardless of soil-fertilization treatment, whereas TH yield efficiency was reduced only in soil-fertilized vines. Soluble solid content of TH and FOL was higher than CTR only in non-fertilized vines, whereas acidity was generally highest in FOL. Both TH and FOL showed better coloring of berries (measured right after thinning) than CTR, regardless of soil-fertilization treatment. These results show that foliar fertilization may substitute for bunch thinning to improve berry quality and at the same time maintain yield of non-thinned vines.