Salinity is one of the critical environmental factors that decreases the water availability and induces nutritional imbalance in crops. In order to study the effect of calcium nitrate [(Ca(NO3)2] in the nutrient solution under salinity conditions, an experiment was designed with different salinity (0, 50, and 100 mM) and Ca(NO3)2 (2, 3, and 4 mM) levels on Cucurbita pepo (zucchini). Based on the results, an increase in the salinity from 0 to 100 mM caused a decrease in the leaf potassium and calcium concentration, whereas the iron, magnesium and zinc concentrations increased. The most effective Ca(NO3)2 level in increasing the nutritional quality and yield of zucchini was 3 and 4 mM. Salinity at 50 and 100 mM significantly increased the leaf sodium concentration and leaf area as well as the leaf number per plant, while the application of both Ca(NO3)2 levels modulated the harmful effects of salinity. The amount of malondialdehyde (MDA), proline and hydrogen peroxide (H2O2) as well as the catalase (CAT) activity increased under the severe salinity conditions, whereas the application of 4 mM Ca(NO3)2 had the potential of removing the negative effects of severe salinity. The catalase activity increased along with the increase in the Ca(NO3)2 concentration, which was independent from the salinity level. However, the amount of proline, MDA and H2O2 decreased in plants fed with 3 and 4 mM Ca(NO3)2 compared to the control in the presence of salinity. These findings suggest that both the 3 and 4 mM concentrations of Ca(NO3)2 under 50 mM salinity could be used to improve the zucchini performance by maintaining the ion homeostasis and inducing the antioxidant defence system.
