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Figure 2. Red Jory Ultisol of Willamette Estate Vineyards in the south Salem Hills, Oregon, USA, where it is developed atop a thick middle-Miocene Oxisol
(lateritic bauxite), red in the vineyards (A), and thick in a nearby quarry (B). The Jory soil series is intensely planted in vines, but comes in two distinct varieties
parented by bauxite or by basalt. Photo A courtesy of Matt Boyington; photo B courtesy of Marli Miller.

GSA TODAY | MAY 2016 than harvest date (vine age, plant spacing, trellising, rootstocks, relationship was found between wine pH and the depth to the
fertilization, canopy management) and of viniculture other base of the clayey (Bw or Bt) horizon in the soil (Fig. 3B). These
than blending (crush methods, destemming, sulphite and relationships have a common cause with soil age, because in
acid addition). Oregon, as elsewhere, pH declines and soil depth increases as soils
develop through time (Lindeburg et al., 2013). Among the soils
Other data compilations used in this study were precipitation studied, there is a significant negative correlation between
records from 1999 to 2012 for Rex Station near Newberg (National minimum soil pH and depth to the base of the clayey horizon
Oceanographic and Atmospheric Administration, 2015), (Fig. 3C). All these relationships are significant at greater than
Oregon vineyard harvest reports (National Agricultural Statistics 99% confidence determined by an ANOVA F test, because more
Service, 2015), and Chehalem Vineyard harvest reports than 20 wines are included within each series.
(Chehalem Wines, 2015).
Within the data assembled, wine pH showed no relation with
SOIL DETERMINANTS OF WINE ACIDITY maximum soil pH, perhaps confounded by different practices of
mulching, cover crop, or fallow at the surface. Wine pH correlated
The main result of this study is discovery of an inverse relation- with neither minimum nor maximum soil clay content, nor
ship between the pH of wine and the minimum pH of the soil in minimum nor maximum cation exchange capacity, again perhaps
which it is grown (Fig. 3A). A comparable but direct (not inverse)

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