Vine and soil determinants of 'Semillon' berry composition

Semillon is a high yielding wine grape variety but berries are often characterised with high pH when grown in warm inland regions of Australia. Semillon berry composition was assessed in vines grown under contrasting irrigation regimes in commercial vineyards of the Hunter Valley and the Murrumbidgee Irrigation Area (MIA), NSW. The MIA is a warm inland region with low humidity while the Hunter Valley is a coastal region with slightly milder temperatures and higher humidity. Across both regions, high berry pH was accompanied by high sugar concentrations and was positively correlated to vine leaf area. There were no overall effects of vine water status on berry composition with the exception of those vines grown without any supplementary irrigation. This resulted in berries with lower total soluble solids, dry weight, pH and higher titratable acidity. Across the vineyards of the two viticultural regions, soil potassium concentrations were the strongest determinant of berry pH. Soil potassium concentrations to a depth of 1 m in the MIA were double that of the Hunter Valley and were accompanied by an average berry pH that was 0.4 units higher in that inland region. These data indicated that canopy as well as soil characteristics have an influence on the composition of Semillon grape berries.