Evapotranspiration modeling – off-season table grape vines grown in bi-annual cycles

The Jordan Valley in Israel is characterized by a hot and dry climate. Those environmental conditions can be taken advantage of for advancement of the harvest date of table grapes which is of great commercial value. In order to achieve this goal vines are grown in two annual cycles: a vegetative summer cycle from May to November (without greenhouse coverage) and a winter reproductive cycle (under greenhouse conditions) from December to April. The objective of this study was to determine seasonal crop water use (ETc) of season and off-season table grape vines grown under unlimited water supply in an arid region and to establish the relationship of crop water use (ETc) to vegetative and meteorological conditions (LAI and ETo). Water use of table grapevines (Vitis vinifera ‘Early sweet’) was measured in 4 drainage lysimeters and 2 weighting lysimeters for 2 growing years; 4 growing seasons (2020-2021). The lysimeters were installed in a 0.27-ha vineyard. The vines were drip irrigated at hourly intervals. The volume of water supplied each day exceeded the estimated vine water consumption by 25-50% to ensure continuous moisture conditions of the soil. The leaf area index (LAI) was measured weekly with the SunScan Canopy Analysis. Meteorological data (ETo) were measured at two stations, one inside and one outside the greenhouse. In addition to evapotranspiration rate, stomatal conductance and rate of photosynthesis were measured once a week. Daily ETc ranged from 0.97 to 2.51 mm day^-1 during March 2021 in the greenhouse, and between 4.4 to 7.6 mm day^-1 during August 2021 without the plastic cover. The seasonal ETc calculated measurements were 106 and 626 mm during the 2021 winter and summer seasons, respectively, while average seasonal crop coefficients (Kc) were 0.23 and 0.53, respectively. LAI-Kc linear regression coefficient was high for the summer measurements (R²=0.83) and low (R²=0.11) for winter season. The results obtained in the summer are consistent with the literature, however, it is necessary to examine in depth the effect of greenhouse and winter conditions on the ETc of the vines. Continued careful collection of the data will in the future allow for nonlinear modeling and prediction of ETc.