AVF Proj. ID: 134
Year Funded: 2001
Category: Cultural Practices - Canopy / Trellis System Manag
Investigators: Nick Dokoozlian

Influence of Row Orientation and Cluster Exposure to Sunlight on the Microclimate and Composition of Cabernet Sauvignon Fruits

The effects of row orientation and cluster exposure to sunlight on the microclimate and fruit composition of Cabernet Sauvignon was studied in a commercial vineyard in the Napa Valley. Eight clusters per vine (one cluster/shoot) were selected for use immediately after berry set. Clusters were divided into two groups of four, with each group located on either the morning exposed (north or east side of the vine row, respectively, for east-west and north-south oriented rows) or afternoon exposed (south or west side of the vine row, respectively, for east-west and north-south oriented rows) portion of the vine row. Four cluster sunlight exposure categories were established: (1) full exposure, (2) moderate to high exposure, (3) moderate to low exposure, and (4) shaded. A positive, near linear relationship was found between berry temperature and PAR incident to the cluster surface following veraison. Fully exposed clusters 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. Berry weight was generally greatest for fully exposed berries and least for shaded berries, regardless of row orientation. Soluble solids followed a similar trend, with the lowest oBrix found in clusters on the east side of N-S rows and the highest clusters grown on the south of E-W rows. Titratable acidity was generally similar among exposure treatments, while malate levels in shaded fruits were significantly greater compared to exposed fruits. Observed differences in both skin anthocyanins and total phenolics among the treatments reflected differences in berry temperature resulting from sunlight exposure; fully exposed clusters on the south (E-W rows) and west (N-S rows) exposures had lower anthocyanin concentrations compared to shaded clusters. 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, total phenolics and malate.

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