Bielorai, H., Division of Environmental Physiology and Irrigation, The Volcam Center, ARO, Institute of Soils and Water, Bet Dagan, Israel
Shalhevet, J., Division of Environmental Physiology and Irrigation, The Volcam Center, ARO, Institute of Soils and Water, Bet Dagan, Israel
Levy, Y., Institute of Horticulture, Division of Citriculture, Gilat Experiment Station. D. N., Negev-2, Israel

Results are reported from a long-term field experiment designed to determine the effect of irrigation water salinity on the yield and water uptake of mature grapefruit trees. Treatments were started in 1970 and consisted of chloride concentrations in the irrigation water of 7.1, 11.4 and 17.1 meq/1 added as NaCl+CaCl2 at a 1 : 1 weight ratio. For the last four years of the experiment, 1973 to 1976, yield was linearly related to the mean chloride concentration in the soil saturation extract weighted according to the distribution of water uptake with depth and time (Fig. 2, Table 1). There was a 1.45% (1.68 Mg/ha) yield reduction for each 1 meq/1 increase in chloride concentration above a threshold value of 4.5 meq/1. This corresponded to a 13.5% (14.7 Mg/ha) decrease per 1 mmho/cm increase in the electrical conductivity of the soil saturation extract above a threshold value of 1.2 mmho/cm. Total water uptake was reduced as salt concentration in the soil increased (Fig. 3, Table 2). In the high salinity treatment, root concentration in, and water uptake from, the lower portion of the root zone were decreased. The maximum electrical conductivity (ECe) measured at the bottom of the root zone was 7.90 mmho/cm similar to the values of EC, obtained by linear extrapolation to zero yield and also to zero water uptake. Salt accumulation in the soil depended on the quantity and salt concentration of the irrigation water, rainfall, and on the amount of leaching. SAR and the Na+ concentration of the soil remained low throughout the experiment (Table 3). No leaf symptoms of either Cl- or Na+ injury were observed. The results indicate an osmotic - rather than a specific ion effect - of salinity on grapefruit yield. © 1978 Springer-Verlag.