Importance of chemical sources in salt-induced salinity on plant growth characteristics in pepper

Salinity is one of the top environmental stresses that restrain plant cultivation and production. Many plant growth and quality factors are negatively affected by soil or water salinity. In the present study, the effects of salinity induced by different chemical salts through nutrient solution were evaluated on the growth and productivity of pepper plants (Capsicum annuum var. annuum) under hydroponic and greenhouse conditions. Pepper seedlings after the 4-leaf stage were transferred to hydroponic medium consisting of 70:30 cocopeat to perlite ratio and received different levels of electrical conductivity (EC) of Hoagland nutrient solution. The following ECs of 1.8 (as control and the Hoagland general EC), 5, and 8 were applied. Various chemical salts were used to induce the two electrical conductivity, including NaCl, KCl, K₂SO₄, and KNO₃-Ca(NO₃)₂. The results showed that pepper growth was adversely affected by the two ECs of 5 and 8 exerted by different chemical salts. In EC of 5, NaCl had the most negative effects on growth parameters of plant height, chlorophyll index, number of leaves and lateral shoots, leaf area, and nutrient profile of leaves. Potassium chloride had exerted the least growth restriction. However, when a mixture of KNO₃ and CaNO₃ was used to create EC of 5, many plant growth parameters were improved compared to control plants (Hoagland solution). In EC of 8, all treatments reduced plant growth parameters compared to control, and the extent of growth reduction was significantly stronger in NaCl and KCl compared to other treatments. Application of KNO₃-Ca(NO₃)₂ to create EC of 8 resulted in better plant growth after control. In contrast to EC of 5, K₂SO₄ in EC of 8 recorded higher growth compared to KCl. The results indicate that salinity tolerance of plants including pepper is a complex issue and depends at least to the composition of various salts and their ratio in root medium.