Data were collected on Thompson Seedless grapevines grown in a weighing lysimeter April until July to refine a model of vine water use and then compare those results with actual water use. In addition, similar data were collected in a Chardonnay vineyard using a VSP trellis system with east/west rows, a Chardonnay vineyard using a quadrilateral cordon trained upon a 3-ft crossarm trellis with north/south rows and a Cabernet vineyard using a VSP trellis with north/south rows. The model was dependent upon the interception of sunlight by the vine and the relationship between light and stomatal conductance. Stomatal conductance also was dependent upon the canopy to air vapor pressure difference. Net radiation, vapor pressure and wind speed were measured above the canopy of all vines and recorded hourly. Once the necessary environmental data had been collected on a specific day and canopy conductance (gc) had been modeled, the data were inserted into a resistance-energy balance equation to calculate vine water use. Lastly, vine water use also was modeled by using the relationship between percent shaded area beneath a vine at solar noon and the crop coefficient. This was done at the above-mentioned locations and at four additional vineyards in which the appropriate crop coefficient had already been determined. There was a linear relationship (r2 = 0.99) between modeled water use and estimated (using ET0 and kcS at the wine grape vineyards) or measured water use (using the weighing lysimeter at the Kearney Ag Center) at all four locations. This linear relationship was obtained using data in which water use ranged from a low of 3 to a high of greater than 60 liters (approximately 1 to 16 gallons) per vine per day. While the modeled daily amounts of water were very close to daily actual water use, hourly values of vine water use (using the weighing lysimeter) were somewhat less so. The relationship between hourly modeled and actual water use of Thompson Seedless grapevines using data from five different dates was linear but the r2 was 0.92. There was a linear relationship between the amount of shaded area measured at solar noon beneath the Thompson Seedless vines within the lysimeter and vine ET and the crop coefficient from the beginning of the growing season until August. This relationship was then used to estimate crop coefficients at vineyard locations where I had already established the appropriate seasonal crop coefficients. There was a linear relationship (r2 = 0.82) between the crop coefficient estimated by measuring shaded area at noon and the crop coefficients I was using on the date the measurements were taken. It is felt that this method of determined non-water stressed crop coefficients would be the most practical means of estimating vine water use. The crop coefficients would then provide an objective method of scheduling vineyard irrigations for growers that would increase water use efficiency and optimize yield and quality.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF1999-10-18 09:46:482017-10-18 09:47:23Modeling Grapevine Water Use