Issue link: http://winesandvines.uberflip.com/i/131907
WineEast Quantity and Quality in a Tunnel How the grapevine can produce both quantity and quality in a high tunnel By Richard Carey I n the March 2013 issue of Wines & Vines, I looked at how growers could use high-tunnel technology to control environmental factors affecting fruit quality, described how a tunnel works and reported the results of a research project that compared vines grown inside a tunnel and vines outside its protection. My article in the April 2013 issue examined the economic impact of using three-season tunnels and discussed factors that should be considered when constructing a tunnel and how they impact grapegrowing. This article will address the question of how tunnels can enable grapevines to provide high yields of high-quality fruit. Many in the grape- and wine-producing communities have seen high yields and superior quality as a difficult prospect to execute in the vineyard, while others such as John Gladstones, Richard Smart and Nick Dokoozian have offered hope that we can have both. From the work presented here, the physiology of the grapevine actually sets up conditions whereby the plant takes advantage of the controlled tunnel environment and allows quality fruit to be produced in larger quantities. The wine industry usually thinks of California's Mediterranean climate, with its warm days and cool nights, as being ideal for growing grapes. Later in this article we will look at what really happens in the grapevine and see that California's cool nights are not really an advantage due to relative reaction rates that take place in the vines' photosynthetic processes. It is possible that a climate with less diurnal variation is preferable for achieving full ripeness in grapes. With less variation between day and night temperatures, the East may be able to produce superior fruit quality at higher yields—especially if other problematic issues can be taken care of by utilizing innovative systems such as high tunnels. If a plant is going to have the energy to produce fruit, it starts with the leaf. Growing wine grapes in a tunnel allows vines to take advantage of the controlled environment to produce quality fruit at larger quantities. Wine East HIGHLIGHTS: • This third article in a series shows how greenhouse tunnels can enable high quality and high quantity for wine grapes. • he author explains how indirect T light in a tunnel differs from direct sunlight on grapevine leaves, enabling more leaves to produce energy. • he author concludes that vines in T tunnels in eastern North America can reach full maturity at lower carbohydrate production, and the grapes will make wines with better balance than in many western Mediterranean-climate growing regions. Remember the structures involved for light capture and their ability to capture that energy and efficiently transfer it to the enzymatic motor that drives plant growth. That structure in the leaf builds everything a grape plant needs to produce its final product: grapes. The impact of irradiance There has been a considerable amount of research investigating the relationship between irradiance intensity on the leaf and production of carbohydrates. One interesting factor about this relationship has been the discovery that for a whole group of plants known as broad-leafed plants (C3 plants), as opposed to grasses (C4 plants), the photosynthetic rate for C3 plants reaches its maximum production of carbohydrates at about 75% of full sun incident radiation. C4 plants do not have this limitation. Thus, for C3 plants, more radiation does not mean there is more carbohydrate production. Above this irradiance, the electrons that are generated cannot transfer their energy to the site of compound production fast enough to make use of that energy. Much like a solar panel that can't deliver its energy to the power grid, it "grounds" out and is lost to thermal increases in the leaf's temperature, and at times the demise of the leaf due to heat. On a bright sunny day, light in the field falls directly on a leaf, and the light impacts the chloroplasts to generate the electrons for energy production. Leaves not directly exposed to this light can still produce energy, but they lose a vast amount of light's direct impact on the leaf that is in a direct line from the sun. Grapes grown in a tunnel that has the correct plastic barrier receive reflected light that is bouncing around the inside of the tunnel. On a clear sunny day I measured the direct incident radiation outside the tunnel at 1 watt Win es & Vi n es JU NE 20 13 75