Effects of soil salinity from long-term irrigation with saline-sodic water on yield and quality of winter vegetable crops

From 1988 onwards a study was carried out to evaluate the long-term effects of increasing water salinity (0%, 0.125%, 0.25%, 0.5% and 1% of commercial NaCl) on some vegetable crops growing in a clay-loam soil. In 1992 and 1993 the effects of the residual soil salinity on yield and some aspects of yield quality were studied in lettuce, endive and fennel grown during irrigation-free seasons on a field which had undergone the same irrigation treatment since 1988. Within the range of electrical conductivity of the saturated-soil extract (ECe) between 2.0 dS m(-1) (treatment 0%) and 6.0 dS m(-1) (treatment 1%) the marketable yield decreased by about 60% in endive and fennel and by about 15% in lettuce which proved more tolerant than the other crops. Gas exchange rates and stomatal conductance were reduced by salinity in lettuce. Soil salinity affected product quality: lettuce and endive appeared to be more sensitive to tipburn and necrotic symptoms occurring in the crop under saline-sodic conditions; fennel heart length, width, and thickness were also significantly reduced and the heart shape tended to be modified in plants grown on salt-affected plots. The results, obtained by analyzing the salt tolerance model of Maas-Hoffman and its descriptive parameters, place lettuce, endive and fennel in the moderately sensitive category. In terms of ECe, the threshold ranged from 1.8 dS m(-1) (fennel) to 2.7 dS m(-1) (lettuce) while the slope varied between 5.8% per dS m(-1) (lettuce) and 15.7% per dS m(-1) (endive).