Investigation of the effect of humic acid applications on seedling development parameters in calendula (calendula officinalis L.) plant grown under different salt concentrations

This study was conducted to determine the effect of humic acid application on seedling growth parameters of marigold (Calendula officinalis L.) grown under salt stress. The research was established in 2024 as a pot experiment in the Field Crops Laboratory of the Faculty of Agriculture, Siirt University. Salinity stress factor (control (0) mM, 25 mM, 50 mM, 75 mM, 100 mM, 125 mM, 150 mM) was applied and various doses of humic acid (0 mL/pot, 1,28 mL/pot, 2,56 mL/pot, 3,84 mL/pot, 5,12 mL/pot and 6,4 mL/pot) were applied to the plants. The experiment was set up in a factorial experimental design in randomized blocks with 4 replications. In the study, the growth parameters of plant height, stem thickness, number of leaves, root length, root thickness, fresh and dry plant weight and chlorophyll content were examined. It was observed that increasing salt concentrations generally had a negative effect on all parameters except root length and root thickness. According to these results, increased salt stress negatively affected plant development, but humic acid applications significantly reduced these negative effects. In conclusion, it was determined that calendula is sensitive to salinity, but humic acid applied at appropriate doses can be effective in increasing salt tolerance. These findings indicate that, especially in the evaluation of saline soils, the use of humic acid at appropriate doses in calendula can help reduce yield losses. It is recommended that similar applications be tested in open field conditions with different medicinal and aromatic plants in future studies.