Issue link: http://winesandvines.uberflip.com/i/172581
s m a r t v i t i c u lt u r e climate. Hotter, sunnier and less humid regions have higher potential evapotranspiration, and well-irrigated crops will lose more water. Examples of these differences include a growing season potential water use of 51 inches in Fresno to 44 inches in the Paso Robles region and 36 inches in Santa Maria. The ratio between the actual vineyard water use and the potential evapotranspiration is defined by the factor kc. This factor varies with stage of the growing season. It is higher later in the season, when vines have reached their full exposed leaf area, and also varies with vine row spacing and trellis system. The factor is higher for close vine rows and for divided trellis systems, both of which have higher amounts of exposed leaf area per acre. A particularly useful part of the research was to develop a relationship between the canopy's shaded area at noon and the crop factor kc. This allowed Dr. Williams to develop irrigation strategies for vineyards of different row spacing and trellis systems and row orientations at various times of the year. His paper documents simple methods as to how kc can be calculated from the noon shadow area. Williams' paper covers many pages in PWV, and this column is only a few hundred words, so the reader should refer to the original article for details. Smart proposals for wine grape irrigation Williams has used pressure-chamber readings as a first point of reference for vine water stress. I do not feel comfortable with this. I am used to working in environments where intermittent cloud cover may occur, and where the effects of dayto-day temperature and humidity variations on mid-day pressure-chamber readings can be dominant. I have found the appearance of the vine to be a more useful indicator for irrigation management. Therefore, my approach has been to use the appearance of grapevines, as quantified by visual scorecards, as an indicator of vine-water status. I have developed two scorecards. The first describes shoot tip growth rate and can be used from fruit set through véraison, about which time shoot trimming has usually occurred. I have been able to quantify the appearance and growth rate of shoot tips to a numerical score, a grapevine stress index if you will. Following véraison, shoot tip growth should not occur, and I have developed a second scorecard that relies on the pr actica l win ery & vin eya r d O CTO B ER 20 13 79