Irrigation of grapevines with saline water. I. Leaf area index, stomatal conductance, transpiration and photosynthesis

In the Negev Desert of Israel, saline water is used to irrigate grapevines (Cabernet Sauvignon grafted on Roggeri) with the premise that the vine is only moderately salt sensitive. The objectives of the research were to study the effect of salinity on major production factors of the grapevine. Irrigation was applied with water of three salinity levels: 1.8, 3.3 and 4.8 dS m^-1 in four replications. Seasonal water application was 633 mm for all treatments. Biweekly measurements were taken from April to October. Green area index (GAI: the ratio of total leaf surface to the unit of land area allocated to each vine), photosynthesis, leaf conductance and transpiration fluxes were determined and the measurements were combined to form an exponential relationship between plant canopy and effective light interception. The effect of salinity was most pronounced on GAI and leaf conductance. Its maximal value (GAI = 5.2) was reduced by about 40% with increased salinity. Gas exchange rates per unit area of individual leaves were less affected by salinity. The extrapolation of the data from daily to seasonal values yielded a total of 9.0, 7.4 and 6.8 Mg ha^-1 for the respective low, medium and high salinity levels. Hence, total grapevine productivity, based on the product of leaf area and the photosynthesis rate declined with increased salinity. Total yield of berries was not reduced by salinity and hence it was concluded that in addition to yield other factors should be studied. For example, the quality of the berries and life expectancy of the vines under saline conditions.