Investigating the effect of humic acid on the morphological and physiological characteristics of rosemary (Rosmarinus officinalis L.) under salt stress

Rosemary is widely used as an ornamental and medicinal plant. Salinity is one of the most important problems for plant production in the world. Knowing the methods that lead to controlling and reducing the effects of salinity in plants is important. The present experiment was conducted as a factorial in a completely randomized design with three replications on three-month-old rosemary plants. The first factor was humic acid treatment (0, 250 and 500 mgL-1) and the second factor was sodium chloride treatment (0, 25, 50 and 75 mM). Based on the obtained results, the minimum length of the main branch (24.41 cm) and the secondary branch (7.68 cm) were obtained in 75 and 50 mM salinity treatments without humic acid, respectively. The highest fresh weight of shoot was in humic acid treatment of 500 mg L-1 + 25 mM salinity, which was not significantly different from humic acid treatment of 250 and 500 mg L-1 without salinity treatment. The dry weight of the branches was influenced by the simple effect of the treatments, so that humic acid 250 mgL-1was effective in increasing the dry weight of the branch, and the highest dry weight of the branch was observed at zero salinity and the lowest dry weight of the branch was observed at 75 mM salinity. The highest content of total chlorophyll and the amount of potassium were obtained in humic acid 500 mg L-1 and the lowest was related to salinity of 75 mM. The amount of proline, ion leakage and sodium percentage were at the maximum in 75 mM salinity without humic acid treatment. According to the obtained results, the use of humic acid 250 and 500 mg L-1 was effective in reducing the negative effect of salinity.