Optimising Tempranillo Grapes Phenolic Composition Through Foliar Applications of Urea at Pre-veraison and Veraison

Abstract The phenolic constitution of grapes has a direct effect on the colour, flavour, and mouthfeel of grapes and wine, thus determining their quality. The objective of this work was to assess the effect of urea foliar application on grape phenolic composition. The trial involved the influence of three urea doses (3, 6, and 9 kg N ha -1 ), which were applied either at pre-veraison (Pre) or veraison (Ver), on Tempranillo grape phenolic profile in two seasons. The control and urea treatments were carried out in triplicate, in a randomized block design. The yield and general grape parameters were not affected by the foliar applications of urea. However, the lower urea concentration improved stilbenes, hydroxycinnamic acids, and flavanols content. The timing of urea application had no significant impact on some of these phenolic compounds. However, urea applied at veraison enhanced their content, especially hydroxycinnamic acids. Additionally, the weather conditions were the main factor that improved the phenolic compounds in grape berries, since warm and dry weather stimulated their synthesis. Consequently, applying a low urea concentration at veraison helps to boost the non-anthocyanin composition of Tempranillo grapes. Therefore, urea foliar treatments can be a good and easy tool in order to increase Tempranillo grape phenolic composition.