Spatial variability of grape composition in a Tempranillo (Vitis vinifera L.) vineyard over a 3-year survey

The study was conducted in a Tempranillo (Vitis vinifera L.) vineyard, in Navarra (Spain) across three consecutive seasons. Winegrape technological (total soluble solids, pH and titratable acidity) and phenolic (anthocyanins and total phenols) variables were measured in a regular sampling mesh at harvest, covering the entire area. Grape phenolic parameters exhibited more variability, in terms of coefficient of variation and spread than total soluble solids and pH, whilst titratable acidity presented a similar variability than grape phenolic attributes. All the grape composition parameters showed spatial structure when omnidirectional variograms were computed. Spatial dependence was found to be high for total soluble solids and acidity, and moderate for anthocyanins and total phenols, which were found to vary at equal or shorter distances than the sampling mesh. Inter-annual stability of the spatial variation pattern was computed by cross-tabulation techniques such as the percentage of pixels well classified (PPWC) and the Kappa index, and was observed only for grape total soluble solids and acidity in the 3 years of study. Phenolic compounds' spatial pattern revealed to be more sensitive to changes in the interactions of the soil-weather-vine system over the three seasons. When factorial analysis was applied, two main factors were extracted. Factor 1 was highly related to total soluble solids and acidity parameters, while factor 2 was mostly explained by anthocyanins and total phenols in the berry. The extracted factors allowed the computation of two main descriptor maps for the entire vineyard in terms of grape composition, given that they were also independent, with different spatial distributions. For each season, factor maps were found as a useful way through selective harvest, as they showed the spatial structure of grape composition and provided integrated information of grape quality. This knowledge would enable viticulturists with a useful tool to identify zones within the vineyard of differential grape composition to be devoted to differential wine styles.