Spatial Variability in Soil and Vine Water Status in Ontario Vineyards. Relationships to Yield and Berry Composition

Grapevine water status of Vitis vinifera cvs. Riesling, Cabernet franc, and Pinot noir was evaluated in Ontario, Canada, using leaf water potential (Psi) and surface soil water content (SSWC; %) to examine spatial relationships between soil and vine water status and berry composition variables, particularly secondary metabolites. The goal was to assess their significance as drivers of the terroir effect. Research was conducted over two vintages (2014 and 2015). Strong inverse relationships were found between vine water status and total phenols in Cabernet franc and Pinot noir and monoterpenes in Riesling. Leaf If was associated with berry size, while yield had strong negative correlations with pH and (in most cases) positive correlations with vine size. Principal component analysis complemented with k-means clustering identified relationships between variables, while Moran's index also indicated strong clustering patterns for SSWC. Both SSWC and leaf If showed weak correlations with each other. Overall, leaf Psi was a stronger indicator of important secondary metabolites (anthocyanins, phenols, color, and monoterpenes) than SSWC.