The terroir of winter hardiness: a three year investigation of spatial variation in winter hardiness, water status, yield, and berry composition of riesling in the niagara region using geomatic technologies

Grapevine winter hardiness is a key factor in vineyard success in many cool climate wine regions. Winter hardiness may be governed by several factors in addition to extreme weather conditions – e.g. soil factors (texture, chemical composition, moisture, drainage), vine water status, and yield– that are unique to each site. It was hypothesized that winter hardiness would be influenced by specific terroir factors of a vineyard, and that vines with low water status [based on leaf water potential (leaf ψ)] would be more winter hardy than vines with high water status (less negative leaf ψ). Six different Riesling vineyard blocks throughout the Niagara Region in Ontario, Canada were chosen. Data were collected every six weeks, at fruit set, lag phase, and veraison (soil moisture, leaf ψ), at harvest (yield components, berry composition), and three times during the winter (LT50; the temperature at which 50 % of the buds die; bud death) in the 2010-12 seasons. Interpolation and mapping of the variables was completed using the kriging interpolation method (ArcGIS 10.1) and statistical analyses (linear correlation, k-means clustering, principal components analysis, multilinear regression) were performed using XLSTAT. Clear spatial trends were observed in each vineyard for soil moisture, leaf ψ, yield components, berry composition, and LT50. GIS and statistical analysis revealed that both leaf ψ and berry weight could predict the LT50 value, with particularly strong positive correlations observed between LT50 and leaf ψ values in most of the vineyard blocks in 2010-11 (4/6 and 5/6, respectively). In the extremely dry 2012 season, leaf ψ (range across sites at veraison 0.9 to 1.4 MPa) was positively correlated to LT50, yield, titratable acidity, pH, and Brix and negatively to soil moisture and monoterpene concentration in Riesling. Overall, vineyards in different appellations showed many similarities (Niagara Lakeshore, Lincoln Lakeshore, Four Mile Creek, Beamsville Bench). These results suggest that there is a spatial component to winter injury, as with other aspects of terroir. Furthermore, this study allows for means by which to compare winter hardiness to other critical variables in order to better understand the terroir of the Niagara region.