Effects of supplementary potassium and phosphorus on physiological development and mineral nutrition of cucumber and pepper cultivars grown at high salinity (NaCl)
Two cucumber (Cucumis sativus) cultivars, Seraset F and Rabina F, and two pepper (Capsicum annuum) cultivars, California Wonder and Charliston 52, were grown hydroponically for six weeks to investigate the effectiveness of supplementary potassium (K) and phosphorus (P) applied to the root zone of plants grown at high (60mM) NaCl concentration. Treatments used in this experiment were (i) control: nutrient solution alone, (ii) high salt: nutrient solution plus 60 mM NaCl, and (iii) high salt with supplementary P and K: nutrient solution plus 60 mM NaCl, 1 mM KHPO, and 2 mM KSO. Supplementary 1 mM KHPO and 2mM KSO was added to nutrient solution for four weeks. Plants grown at high salt produced less dry matter and chlorophyll than those in normal nutrient solution for both cucumber and pepper cultivars. Reductions in both dry matter and chlorophyll concentrations were greater for pepper than cucumber. Supplementary K and P restored dry matter and chlorophyll concentrations for both species to levels similar to the control. Membrane permeability increased with high salt application and these increases were greater for pepper. Supplementary K and P restored membrane permeability in both species to levels similar to the control. Plant daily water use was decreased by high salt but it was restored with supplementary K and P to levels similar to the control. Sodium (Na) concentration in plant tissues increased for both species in the high salt treatment. Concentrations of P and K were in the deficient range in the plants grown at high salt and supplementary K and P application corrected these deficiencies.