|Perez Pena, J|
Submitted to: Agriculture and Forest Meterology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2005
Publication Date: 2/16/2006
Citation: Tarara, J.M., Ferguson, J.C., Hoheisel, G.A., Perez Pena, J.E. 2006. Asymmetrical canopy architecture due to prevailing wind direction and row orientation creates an imbalance in irradiance at the fruiting zone of grapevines. Agricultural and Forest Meteorology. 135:144-155. Interpretive Summary: Grapes are a high-value crop commanding premium prices for the farmer if certain quality traits are met, many of which depend directly on the amount of sunlight the fruit is exposed to during ripening. Thus, grape growers spend much time and many resources ensuring that the shoots and leaves (vegetation) are relatively balanced between the two sides of the grapevine so that the fruit on either side of the vine is exposed to equal intensity and duration of sunlight. Rows typically are oriented north to south so that the vine has an east and a west side, each of which receives equal sunlight exposure over the course of a day. In windy areas, shoots may grow contrary to the direction desired by the farmer for a balanced vine canopy between the east and west sides of the row, depending upon the direction from which the prevailing winds blow. When orienting rows in new vineyards, growers should consider that both compass direction and the prevailing wind might create an imbalance in vine vegetation that could lead to excessive sunlight exposure on one side of the row. Conversely, in established vineyards where row orientation cannot be changed but is set for the lifetime of the vineyard, growers may need to consider alternative trellising techniques or other management options to cultivate a slightly more shady canopy (more vegetation) on the windward side of the vine, because the windward side would be most prone to excessive sunlight exposure and concomitant risk of lesser fruit quality.
Technical Abstract: Much effort is invested in trellising and training grapevines to balance the exposure of fruiting zones on both sides of the canopy to solar radiation. In windy sites, thigmomorphogenesis in annually renewed shoots can reshape a bilaterally balanced canopy depending upon the angle of attack of the prevailing wind. In two contiguous vineyards differing only in row orientation, irradiance at the fruiting zone and shoot geometry were measured. Prevailing west-southwest winds were roughly parallel to the rows of one vineyard and at an oblique angle to the rows of the second vineyard. Mean wind velocity in the prevailing direction was 3.3 m s-1 during the growing season. Shoots were grouped into four classes based on row orientation and shoot azimuth from the cordon. Mean internode length per shoot did not vary between shoot classes and was not related to row orientation. Windward shoots were significantly shorter than all other classes of shoots because of fewer nodes per shoot. Regardless of row orientation or initial shoot azimuth, shoot tips tended to be displaced eastward (leeward). In rows oriented north-south (oblique angle to the prevailing wind), vines did not form a uniform canopy about the cordon, resulting in higher irradiance at the fruiting zone on the windward (west) side of the canopy, which could result in unequal berry ripening, particularly under high irradiance and high temperatures. Results suggest that in consistently windy locations, growers should establish row orientation based both on sun-earth geometry and on the consequences of radiation distribution at the fruiting zone due to wind-induced canopy asymmetry, or they should compensate for non-uniform canopy architecture with modifications to the trellis system and standard training practices.