Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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MAY/JUNE 2010
WINEGROWING
Days After Budbreak/Shoot Demand graph
Figure 1. VitiSim simulations of the seasonal carbon demand for shoot growth by growing shoots on Concord vines with 100 shoots or 350 shoots per vine and long-term Geneva, NY weather. Note the shift in peak demand.
expected to be a better metric of vine capacity than pruning weight. It is assumed that exposed leaf area reflects light interception, but in the vineyard it is difficult to estimate the exposed leaf area (how much exposure is “exposed”?) and average leaf function due to the complexity of the grape canopy.
Alain Carbonneau developed a practical method in 1995 to estimate vine capacity based on the surface area of varying trellis systems.4 However, this approach is limited by its assumptions of uniform photosynthetic functionality across the exposed canopy.
In practice, most grapegrowers and viticulturalists discuss “crop load,” i.e. the ratio of vine capacity to the demand of the crop, rather than “vine balance.”
Measuring crop load requires estimations of both vine capacity and crop demand. “Yield/pruning weight” or “leaf area/g of fruit” address this balance and are useful expressions for estimating crop load. However, they are limited for the aforementioned reasons and do not address seasonal dynamics.
Integrating the many complex processes in a dynamic environment requires dynamic models. Sunlight energy absorption, carbon production and utilization are the best-understood processes, and they have been successfully modeled in many plants. The lead author has developed a simplified carbon balance model to evaluate the seasonal dynamics of the carbon component of vine capacity and demand for carbon.8,9,10
Seasonal dynamics of vine balance and crop load
A simplified dynamic carbon balance model, developed initially for apple trees, was adapted for grapevines using STELLA®, an easy-to-use auto-programming software. The model (VitiSim) uses a daily time step to simulate seasonal leaf area development, vine light interception, canopy photosynthesis, canopy respiration, total dry matter accumulation, and dry matter distribution to competing vine organs (leaves, roots, fruit, etc.).
From this data we can: a) develop seasonal curves of the growth, vine capacity, and demands of various organs and estimate balances between their supplies and demands;
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