Influence of Row Orientation and Cluster Exposure to Sunlight on the Microclimate and Composition of Cabernet Sauvignon Fruits
The effects of row orientation and canopy density (as defined by leaf layer number or LLN in the fruit zone) on the fruit zone microclimate and composition of Cabernet Sauvignon was studied in a commercial vineyard located near Oakville, CA in the Napa Valley. A mature Cabernet Sauvignon vineyard with adjacent blocks of north-south and east-west oriented rows was used. Fruit zone microclimate was manipulated within each row orientation immediately after berry set by varying the amounts of basal leaf and lateral shoot removal in the fruiting zone (primary shoot basal nodes 1-5). The following four treatments were applied: 1. untreated control; 2. remove basal leaves only; 3. remove lateral shoots only; 4. remove basal leaves and lateral shoots. The LLN values created by these treatments ranged from 0 (complete basal leaf and lateral shoot removal) to approximately 2.5 (untreated) in the fruit zone. A negative, near linear relationship was found between fruit zone LLN and the percentage of exterior clusters in both row orientations. The percentage of exterior clusters ranged from approximately 30%(LLN~2.5) to over 90%(LLN=0). Berry temperature and cluster sunlight exposure increased as LLN in the fruiting zone declined. Fully exposed clusters (LLN=0) on the south (E-W rows) and west (N-S rows) sides of the canopy had the greatest mid-day berry temperatures in the experiment, averaging approximately 6C greater than ambient air temperature by late afternoon on most sunny days. Berry weight was generally least for fully exposed berries and greatest for shaded berries, regardless of row orientation. In N-S rows, soluble solids were lowest in fully exposed berries and increased slightly as LLN increased. No trend was observed between cluster exposure and soluble solids levels in E-W oriented rows. Titratable acidity and malic acid content generally declined as cluster exposure increased, while juice pH increased slightly as cluster exposure increased. Observed differences in skin anthocyanins in N-S rows reflected differences in berry temperature resulting from sunlight exposure; fully exposed clusters on the west exposure had lower anthocyanin concentrations compared to partially shaded clusters. No strong trend in berry color development due to cluster exposure was observed in E-W rows, although fruit in E-W rows generally had greater color development for all exposure levels compared to fruit in N-S rows. The results indicate that berry exposure to direct sunlight during the afternoon (west or south facing exposures) leads to elevated berry temperatures and undesirable reductions in berry color and acidity. Chemical and sensory analyses of experimental wines produced from each treatment will be completed during the spring of 2002.
