Nutrient uptake, proline content and antioxidant enzymes activity of pepper (Capsicum annuum L.) under higher electrical conductivity of nutrient solution created by nitrate or chloride salts of potassium and calcium

This study was conducted to evaluate the effects of higher conductivity of nutrient solution created by nitrate or chloride salts of potassium and calcium on growth characteristics of pepper plants (Capsicum annuum var annuum) during four months of growth period. Two EC5 and EC8 dS/m of Hoagland nutrient solutions were prepared using various salt combinations, namely: KCl + CaCl2, KNO3 + CaNO3, and KNO3 + CaNO3 + NaCl. Hoagland nutrient solution with EC 1.8 dS/m served as a control. Higher conductivity treatments had different effects on pepper plant growth. The most significant reduction in growth parameters of plant height, shoot fresh weight, fruit yield and nutrients uptake was in plants treated with KCl + CaCl2 particularly at EC8. Application of KNO3 + CaNO3 particularly at EC5, showed no difference as compared to the control regarding many growth parameters. Application of KNO3 + CaNO3 at EC5 resulted in higher shoot fresh weight compared to the control. All salinity treatments, except from KNO3 + CaNO3 at EC5, reduced the fruit yield compared to the control. Treatments of KCl + CaCl2 and KNO3 + CaNO3 + NaCl particularly at EC8 of nutrient solution, resulted in higher leaf proline concentration, catalase and peroxidase enzymes activity compared to the control. Other conductivity treatments showed no difference in catalase or peroxidase enzymes activities. Significantly the lowest amount of leaf N, K, Mg and Ca was in KCl + CaCl2 at EC8. On the other hand, the highest leaf macronutrient concentrations were in KNO3 + CaNO3 at EC5 and/or EC8 that showed only higher leaf N and Ca values compared to the control. Leaf micronutrient concentrations were the highest in KNO3 + CaNO3 at EC5 that generally showed no difference with control plants. However, application of KCl + CaCl2 particularly at EC8 and to less extent KNO3 + CaNO3 + NaCl at EC8, reduced the leaf micronutrient concentrations. Application of KNO3 + CaNO3 at EC5 increased and KCl + CaCl2 or KNO3 + CaNO3 + NaCl at EC8 decreased the leaf Fe concentration compared to control plants.