The disjointed influence of soil and climate on grape productivity and quality. An assessment by OMCIA-PLSR statistics on a case study in southern Italy

This paper reports the results of an investigation aiming to assess: i) the influence of soil and/or climate on the qualitative and quantitative features of grape, and, ii) the consistency of soil-wine-grape relationships under contrasting climatic conditions. The grapes were from Falanghina which is a relevant autochthonous vineyard of Southern Italy. To stress results, the analysis considered two different years (2002 and 2003), characterised by very contrasting climatic conditions in terms of both rain and temperature. Differences in the mean values of grape characteristics from one year to another were statistically evaluated using the usual student t-test. Relationships between soil properties and 2002-2003 grape variables were then simultaneously evaluated using the explorative OMCIA-PLSR statistics. OMCIA-PLSR is a new multivariate statistical method for making predictive models and belonging to the class of the explorative data analysis. Titratable acidity (TAc) and malic acid (Mal) were positively correlated to soil total nitrogen (N), exchangeable potassium (K), and organic carbon (OC), whereas tartaric acid (Tar) was negatively related with soil exchangeable calcium (Ca), pH and carbonates (CaCO3). Statistical analysis revealed that the mean weight of cluster and berry did not change during the investigated period, as well as the structure of relationships between soil and grape variables was highly comparable and consistent from one year to another. Contrastingly, the values of grape compositional compounds, as TAc, Mal, tartaric acid (Tar), soluble solids (Brix) and grape pH (GpH) varied significantly from 2002 to 2003 vintage. Results showed that soil and climate independently affect quantitative and qualitative grape features, respectively.