The influence of vine vigour and crop load on Sauvignon blanc vine growth and fruit composition in Marlborough, New Zealand

Aims: Sauvignon blanc is the flagship wine of Marlborough, with its style described as the definitive benchmark of the varietal. The majority of Marlborough’s vineyard plantings are in the Wairau plain; where the young alluvial soils were formed by sedimentation from the Wairau River. The braided nature of the river and frequent flood events has created significant vertical and horizontal soil texture variation. This soil texture variation has been shown to reflect changes in trunk circumference, which lead to the use of trunk circumference as an indicator of soil texture. The aim of this study was to investigate the impact of soil texture and yield on vine performance and fruit composition, within a single vineyard. Methods: Trunk circumference measurements were grouped to create five vine size classes, while two pruning methods (two and four-cane VSP) were applied to create two crop load treatments with two different canopy types. Vine vigour, canopy density, vine phenology, yield and fruit composition measurements were taken from each vine size and crop load treatment throughout the season. Results: Vine vigour and canopy density increased with increasing vine size while increases in crop load resulted in decreased vigour and increased canopy density. Vine phenology was delayed with both increasing vine size and increasing crop load. Vine size did not influence yield but did influence fruit composition; increases in vine size delayed ripening with lower soluble solids and higher titratable acidity levels measured at harvest. Crop load influenced both yield and fruit composition with increases in crop load leading to higher yields and delayed ripening. Lower soluble solids and higher titratable acidity levels were measured at harvest as crop load increased. Conclusions: The variation in soil texture found in the Squire Vineyard lead to variation in vine vigour, canopy density and phenology. These differences in vine growth had no influence on vine yield but did have a significant impact on fruit composition at harvest. Variation in vine growth and fruit composition within a single vineyard creates challenges with vineyard management; particularly with canopy management, irrigation, nutrition, and harvest decisions