The overall goal of this project is to understand differences in soil properties that contribute to significant differences in vine vigor, fruit yield and properties, and ultimately wine quality. Our collaborators at J. Lohr identified a unique opportunity to study a single vineyard consisting of four separate plots, each planted with Cabernet Sauvignon grapes on their own roots. The plots are managed in an identical manner. Wines made from these four plots had different sensory characteristics in an informal tasting, and preliminary field studies revealed four distinct soil types in the different vineyard plots.
During the past year, we have made excellent progress in accomplishing the objectives of this grant. Briefly, these objectives were: (1) to study variation in soil physical and chemical properties between the four sites; (2) to study differences in plant growth and yield between the four sites, and relate these differences to soil variability; and (3) to study differences in berry juice and wine quality between the four sites, and if possible relate these to soil variability. Thanks to outstanding collaboration from J. Lohr Vineyards, we opened eight sampling pits (two per site), and obtained multiple replicate samples from each site for chemical and physical analysis. Soil moisture probes and suction devices for obtaining soil solution samples were implanted in each site. Canopy temperature sensors were also set up, and the locations of sampling sites were georeferenced for mapping purposes. We obtained vine leaf and petiole samples throughout the growing season (bloom, veraison and harvest) from each site and are currently analyzing these tissues. We also measured vine diameters, pruning weights, cluster weights at harvest and cluster numbers. Small lot wines have been made from grapes at each site and will undergo thorough chemical and sensory analysis.
Soil solution chemistry, plant chemistry and wine chemistry analyses are underway. Our results to date indicate clear differences in soil properties between sites. The soils at the four sites fall into three distinct categories: two different types of Alfisols, a Mollisol and a Vertisol.