Water requirements of table grapes in an arid site

New varieties of seedless table grapes have been introduced in Arizona and their water requirements need to be obtained in order to optimize water use. A field experiment was carried out in Tucson, AZ, on two varieties: Glenora and Reliance, six years old and irrigated with a drip system. Measurements started on March and lasted till the beginig of July, 1997. The objectives of the study were the determination of the transpiration rate (Tr) and the crop coefficient (Kc) of these varieties. Sap flow gauges were used for measuring the Tr and the crop evapotranspiration (Etc) was obtained from concurrent measurement of a water balance by using a neutron probe and TDR. In the period of 6 to 10 of June 1997, the mean Etc of the Reliance reached 7.6 mm/d, while that of the Glenora was 7.5 mm/d. The mean Tr in that period were equal to 3.53 mm/day and 5.56 mm/day for Glenora and Reliance, respectively. During June the mean Tr of the Glenora was approximately equal to 55% of its Etc, and 60% in the Reliance. One important result is that while the soil remains exposured to the sun the soil evaporation is high, despite the irrigation system used. The feasibility of using sap flow gauges for measuring transpiration in table grapes plants was confirmed.