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Days After Budbreak/Crop Demand graph
Figure 2. VitiSim simulations of the carbon demand for crop growth of Concord vines with 100 shoots or 350 shoots per vine and long-term Geneva, NY weather.
b) evaluate the effects of daily weather or longterm climate patterns and different stress and cultural factors on these patterns; and c) try to determine if and when critical periods of carbon supply and demand occur, especially in relation to fruit development and ripening.
Seasonal demand dynamics
In mature vines, the vast majority of net seasonal dry matter assimilated goes into current growth (leaves, shoot stems, and crop). In this example, we present model simulations of healthy, unstressed, heavily-cropped Concord grapevines (spaced 8 x 9 feet) with industry standard 100 shoots per vine (yield of about 9 tons per acre) compared to minimally-pruned vines with 350 shoots per vine (yield of about 12 tons per acre).
Seasonal patterns of supply and demand are distinct. The carbon demand of growing shoots show a single peak around or after bloom. This peak demand occurs earlier in vines with higher node numbers and later in vines with fewer shoots that grow longer into the season (Figure 1). The demand pattern for the crop is a double peak, with a peak a few weeks after bloom during berry cell division, followed by a decline during the lag period (Figure 2).
After veraison, the second peak of demand occurs very rapidly, and then declines with ripening. Shoot numbers affect the timing of peak demand. However, different crop levels affect the amount, but not the timing, of crop
demand in our simulation. Root growth patterns have been reported to be variable, but likely reflect a weak sink throughout the growing season.6
Seasonal carbon supply and supply/demand balances
The seasonal pattern of supply is relatively simple, peaking between bloom and veraison. Supply is affected primarily by total light interception. Since light interception depends on leaf area, more shoots will lead to more rapid canopy development and an earlier peak in canopy photosynthesis (Figure 3).
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