Issue link: http://winesandvines.uberflip.com/i/830382
June 2017 WINES&VINES 53 PRACTICAL WINERY & VINEYARD GRAPEGROWING C ommercial grapegrowers strive to produce the maximum profitable yield of grapes at the composition required to produce wine of a target style that meets quality expectations of consumers. However, this must be done consistently. Since grapevines are perennial plants, the yield must be achieved without negatively influencing the vine's capability of producing a crop in subsequent years. To achieve the correct balance between fruit yield and root and shoot growth, viticulturists need to enable the current season's crop to ripen without "stealing" from vine reserves and negatively affecting next year's crop. When contemplating vine balance, the factors that deter- mine the capacity of the vine to fix carbohydrates (sugars) through the process of photosynthesis and to accumulate inorganic nutrients for growth need to be considered. The rate of photosynthesis and the ability of vines to fix carbohydrates largely reflects the environment in which the vine is growing (warmer sites with increased sunlight and a longer growing season will generally have greater capacity to accumulate carbohydrates). However, vine photosynthesis can be manipulated by growers with the selection of vine- training systems, vineyard design and spacing. For example, the development of divided canopy-training systems has been shown to simultaneously increase potential yield and improve fruit composition. 24 The systems increase the intercepted solar energy and enhance the ability of vines to fix photosynthates, thereby increasing their capacity. At the leaf level, light saturation (the point at which in- creasing light intensity does not further increase the rate of photosynthesis) reaches its maximum at about 1,000 µmol m -2 s -1 . 14 However, in the field, higher light intensities may continue to increase the rate of vine photosynthesis as light penetrates farther into the canopy, increasing the photosyn- thetic rate of leaves underneath the outer layer of leaves. 22 In addition to site effects, the available energy changes both between and within a growing season. Early in the season, temperatures are generally lower than mid-season, and day length is shorter. At the same time, the canopy is still developing. Early, rapid shoot and leaf development at this time often reflects the carbohydrate and nutrient reserves accumulated in the trunk and root system the previous year. Similar incoming energy reductions are observed in the au- tumn, although by this time, the canopy should be full size. Fixed photosynthates now are accumulated in the fruit as it ripens. However, to ensure adequate over-wintering, reserves of carbohydrates and nutrients have to build in the roots and trunk at the same time. In many cool climates, leaf senescence coincides with harvest, thus it is important to build up reserves in the trunk and roots by this time. 1 In warmer climates, where leaves remain functional post- harvest, the reserves can accumulate during this period. For this reason, the timing of leaf senescence in relation to the date of harvest is a key difference between warm and cool-climate viticulture. While this review largely considers the role of photosyn- thates in vine balance, other environmental and biotic factors must be well managed. The professional grower must mini- Grapevine Triangle An aid to understanding grapevine balance By Mike Trought Own-rooted vines in Chile are planted 1.5 to 1.8 meters apart. The roots on the 10-year-old vines reach a depth of 5 to 6 meters. MIKE TROUGHT