Water use of mature Thompson Seedless grapevines in California

Abstract

Water use of Thompson Seedless grapevines was measured with a large weighing lysimeter from 4 to 7 years after planting (1990–1993). 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 in the last 2 years. Maximum leaf area per vine at mid-season ranged from 23 to 27 m2 across all years. Reference crop evapotranspiration (ETo) averaged 1,173 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 for the remaining 3 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 (K c) calculated during the first year (1990) was 0.87. The maximum K c in 1991, 1992, and 1993 was 1.08, 0.98, and1.08, respectively. The maximum K c in 1991 and 1993 occurred during the month of September, while that in 1992 was recorded during the month of July. The seasonal K c followed a pattern similar to that of grapevine leaf area development each year. The K c was also a linear function of leaf area per vine using data from all four growing seasons. The decrease in K c 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.