Influence of soil type and changes in soil solution chemistry on vine growth parameters and grape and wine quality in a central coast California vineyard

The objective of this study was to determine the influence of four soils with contrasting chemical and physical properties on vine growth parameters and wine chemistry in a Paso Robles, California Cabernet Sauvignon vineyard. The selected soils covered contiguous vineyard patches planted with the same cultivar, on its own roots. Furthermore, these vineyards contained vines of the same age that have received the same management practices. The soils belonged to the orders Alfisols, Mollisols and Vertisols. Soil heterogeneity in this vineyard was attributed to variability in soil parent material, originating from old Estrella River alluvial deposits, which ranged from cobbly and gravelly to fine-grained alluvium. Soil moisture was recorded throughout the growing season. Plant water potentials at pre-dawn and midday were monitored on vines growing at two sites per soil type. Vine growth parameters were recorded along with leaf and petiole sampling for tissue analysis. Nutrient balance in the soil solution was characterized at the onset, mid-point and harvest time during the growing season and analyzed in relation to growth parameters and fruit yield. Soil solution concentrations of macronutrients, such as K and NH₄/NO₃, were related to differences in soil pH, organic matter, and clay mineralogy. Petioles and blades were sampled at bloom, veraison and harvest to evaluate plant nutrient concentrations and the relationship to nutrient availability in the soil solution. Variability in soil physical and chemical properties determined cation exchange capacity and nutrient availability in the soil solution, and these properties were found to be related to vine vigor and differences in fruit yield and quality between soils.