The soils situated in the four vineyard blocks have been found to differ significantly in chemical and physical properties. The soils in Blocks 56 and 57 were classified as related Alfisols. The soils in Block 57 had a loam/sandy loam topsoil and a clayey subsoil with an abrupt textural change. These soils were characterized as fine, smectitic, thermic Typic Palexeralfs. The swales in Block 56 contained shallower, less developed Alfisols characterized as fine-loamy, mixed, superactive, thermic Typic Haploxeralfs. These soils had a strong argillic horizon but coarse fragments were also present. The soils in Block 53 were classified as Vertisols; these were fine, smectitic, thermic Haploxererts. These soils were characterized by greater than 30%clay content and a tendency to “shrink/swell” behavior. On the upper part of the topography, the soils in Block 52 were characterized as Mollisols; these were fine-loamy, mixed, superactive, thermic Calcic Haploxerolls. These soils, found primarily on knolls in the landscape, had calcareous seams, laminar lime concretions and an angular blocky structure in the subsoil.
Soil chemistry analyses revealed several striking differences between sites. Notably, the Mollisols and Vertisols had low K+ availability throughout the profiles. Potassium levels were higher in the Alfisols, but only in the superficial horizons. Soil extract Nitrogen and Phosphorous were also comparatively low in the Mollisols. Electrical conductivity, on the other hand, was particularly high in the Ca-rich Mollisols and increased with depth.
The Alfisol (Palexeralf) in Block 57-5 and the Mollisol in Block 52-3 gave contrasting results in terms of vine, fruit and juice characteristics. Vines grown in the Palexeralf had the following characteristics: average to high vine diameters; the highest fruit yield per vine in terms of weight and cluster number of any vines studied; the highest cluster weight of any vines studied. Finally, juice from these vines had the highest °Brix and lowest total acidity of any in the study. In contrast, vines grown in the Mollisol had the lowest vine diameters of any in the study; they also had the highest root density at depth, the lowest fruit yield per vine (in weight), and the lowest berry cluster weights of any in the study. Juice from these vines had the lowest °Brix of any in the study and among the highest total acidity values. Juice properties were surprisingly consistent over two years of study. Blinded sensory analysis of berries from Year 1 revealed an apparent clustering of sensory characteristics along with soil type, and additional sensory analyses are in progress.
Vines grown on the two other soils, the Vertisol in Block 53 and the Haploxeralf in Block 56, showed intermediate characteristics. Vines grown in Block 53 had above average vine diameters, an even root distribution throughout the profile, and average fruit yield. Juice from these grapes had low °Brix and the second highest Total Acidity of any in the study. Vines grown in Block 56 had average vine diameters, high root density near the soil surface, below average fruit yield per vine, and average berry cluster weights. Juice from this site had the second highest °Brix and the second lowest Total Acidity.
Thus, in this study comparing Cabernet Sauvignon grapes of a single clone, on its own roots, grown in four distinct soil types within a single vineyard, vines grown on contrasting soil types had different growth characteristics which were reflected in differences in fruit yield and juice characteristics. Although analysis of data from Year 2 is ongoing, preliminary findings suggest that many of the trends observed in Year 1 are indeed consistent from year to year.
A third year of sampling and analysis will be essential in order to confirm (or refute) these apparent trends. A major emphasis of our work in Year 3 will be to use statistical tools (i.e., multivariate analysis) to determine the extent to which differences in soil physical and/or chemical properties are related to differences in plant growth characteristics, and to grape and wine sensory and/or chemical properties.