Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2002
Publication Date: 3/18/2003
Citation: Irrig. Sci (2003) 22:1-9 Interpretive Summary: Accurate scheduling of irrigation can reduce water use and increase crop yield and quality. Using a weighing lysimeter, a precise method of measuring the water use of a crop, the water requirements of grapevines was measured over 4 years. The water use was related to weather factors that affect evaporation (potential evapotransporation, ETo) to develop a crop coefficient for the grape vines. The vines in the lysimeters used about 850 mm of water each year. The seasonal crop coefficient begins low as the vine begins to leaf out, then increases through the season as the vine grows to a value of about 1.0. The crop coefficient varies with how the vines are trellised and managed. With the coefficient and ETo, which is available to growers in most western states, growers can precisely schedule irrigations for their vines, resulting in efficient water use and high yields.
Technical Abstract: Water use of Thompson Seedless grapevines was measured with a large weighing lysimeter from four to seven years (1990 to 1993) after planting. Above ground drip irrigation was used to water the vines. Vines growing within the lysimeter were pruned to four and six fruiting canes for the 1990 and 1991 growing seasons, respectively, and eight fruiting canes the last two years. Maximum leaf area per vine at mid-season ranged from 23 to 27 m2 across all years. Potential ET (ETo) averaged 1173 mm between budbreak and the end of October each year with a maximum daily amount of approximately 7 mm each year. Maximum daily vine water use (ETc) was 6.1, 6.4, 6.0, and 6.7 mm (based upon a land area per vine of 7.55 m2) for 1990,1991, 1992 and 1993, respectively. Seasonal ETc was 718 mm in 1990 and ranged from 811 to 865 mm the remaining three years of the study. The differences in water use among years were probably due to the development of the vine's canopy (leaf area) since they were pruned to differing numbers of fruiting canes. These differences were more pronounced early in the season. Soil water content (SWC) within the lysimeter decreased early in the growing season, prior to the initiation of the first irrigation. Once irrigations commenced, SWC increased and then leveled off for the remainder of the season. The maximum crop coefficient (kc) calculated during the first year (1990) was 0.87. The maximum kc in 1991, 1992 and 1993 was 1.08, 0.98 and 1.08, respectively. The maximum kc in 1991 and 1993 occurred during the month of September, while that in 1992 was recorded during the month of July. The seasonal kc followed a pattern similar to that of grapevine leaf area development each year. The kc also was a linear function of leaf area per vine using data from all four growing seasons. The decrease in kc late in the 1991, 1992 and 1993 growing seasons, generally starting in September, varied considerably among the years. This may have been associated with the fact that leafhoppers (Erythroneura elegantula Osborn and E. variabilis Beamer) were not chemically controlled in the vineyard beginning in 1991.