Comparative effects of NaCl and CaCl2 salinity on cucumber grown in a closed hydroponic system

The objective of this study was to discriminate among Na, Cl, and Ca salinity effects on cucumber (Cucumis sativus L.). Cucumber plants grown in perlite were exposed for 134 days to low and moderate levels of salinity induced by the addition of either NaCl or CaCl2, at equal rates (on a chemical equivalent basis) to a standard nutrient solution for cucumber up to two target electrical conductivity (EC) levels (3.0 and 5.0 dS.m(-1)). The experimental treatments included also a control, which was irrigated with the standard nutrient solution without additional salt. The mean EC values in the drainage solution were 2.35, 3.94, 4.2, 6.31, and 6.35 dS.m(-1) for the control, low NaCl, low CaCl2, high NaCl, and high CaCl2 treatments, respectively. The fresh and dry weights of stems and leaves were reduced only under conditions of high NaCl salinity, whereas root mass was not affected. Fruit yield decreased in proportion to the increase in NaCl salinity, while CaCl2 salinity reduced yield only at the high EC, to a level that corresponded to the low NaCl salinity. The suppression of yield with increasing salinity resulted mainly from a decrease in fruit size, while the number of fruit per plant was reduced to a lesser extent. These changes caused a reduction in the number of Class I fruit and an increase in nonmarketable produce. Both salinity sources enhanced the total soluble solids and the fruit chlorophyll concentration. NaCl salinity appreciably raised the concentrations of Na and Cl in young and old leaves, and suppressed the K concentration CaCl2 salinity increased leaf Cl and Ca levels and diminished Mg and K. It is concluded that cucumber is more susceptible to NaCl salinity than to equal EC levels of CaCl2 salinity.